Effortlessly calculate the expected weight of your polybags.
Polybag Weight Calculator
Density of the plastic material (e.g., PE, PP) in kg/m³ or g/cm³. Ensure consistent units.
Width of the bag in meters.
Height (or length) of the bag in meters.
Depth or thickness of the bag material in meters (e.g., 0.1 mm = 0.0001 m).
Estimated Polybag Weight
0.00
Bag Volume (m³)
0.00
Material Volume (m³)
0.00
Weight (kg)
0.00
Formula Used: Weight = Material Volume × Density. The Material Volume is calculated by summing the volumes of the faces and sides of the bag, accounting for its thickness.
Weight vs. Material Density
Chart showing the calculated polybag weight at different material densities, holding other dimensions constant.
Polybag Weight Breakdown
Example Breakdown: Weight Calculation for a Standard Polybag
Component
Dimensions (m)
Surface Area (m²)
Volume (m³)
Weight (kg)
Front Face
0.00
0.00
0.00
0.00
Back Face
0.00
0.00
0.00
0.00
Side Panels (x2)
0.00
0.00
0.00
0.00
Bottom Panel
0.00
0.00
0.00
0.00
Top Opening (Overlap considered)
0.00
0.00
0.00
0.00
Total Calculated Weight
0.00
Understanding the Polybag Weight Calculator
What is Polybag Weight Calculation?
Polybag weight calculation is the process of determining the expected mass of a plastic bag based on its physical dimensions, the type of plastic material used, and its density. This calculation is crucial for various industries, including packaging, manufacturing, agriculture, and logistics. It helps in cost estimation, material planning, inventory management, and ensuring that bags meet specific weight-bearing requirements. Accurately estimating polybag weight allows businesses to optimize their production processes, control material costs, and prevent issues related to under- or over-specification of packaging materials. This {primary_keyword} tool simplifies this complex task, providing instant, reliable estimates.
Those involved in sourcing plastic films, manufacturing polybags, or filling them with products can greatly benefit from this calculator. This includes procurement managers, production supervisors, quality control specialists, and even small business owners who need to understand the cost implications of their packaging. A common misconception is that all plastic bags of the same size weigh the same; however, the type of plastic (e.g., LDPE, HDPE, PP) has a significantly different density, directly impacting the final weight and cost. Furthermore, the thickness or gauge of the material is a primary determinant of weight.
Polybag Weight Formula and Mathematical Explanation
The fundamental principle behind calculating polybag weight is the relationship between volume, density, and mass (weight). The formula is derived from the basic physics equation:
Weight = Volume × Density
However, calculating the "Volume" for a polybag requires careful consideration of its geometry. A polybag is essentially a three-dimensional object formed from a sheet of plastic, typically sealed on three sides and open on one, or sealed on all four sides to form a pouch. The volume calculation needs to account for the thickness of the plastic material itself, not just the internal capacity the bag might hold.
To determine the weight of the polybag material, we first need to calculate the total surface area of the plastic used and then multiply it by the thickness to get the volume of the material. Finally, this material volume is multiplied by the density of the plastic.
Let's break down the calculation:
Calculate Surface Areas: A typical polybag has a front face, a back face, two side panels, and a bottom. We assume the width and height are the primary dimensions of the flat, unfolded bag. The thickness (depth) is the gauge of the plastic film.
Front Face Area = Bag Width × Bag Height
Back Face Area = Bag Width × Bag Height
Side Panel Area (each) = Bag Height × Bag Depth (thickness of the material at the side)
Bottom Panel Area = Bag Width × Bag Depth (thickness of the material at the bottom)
The calculator uses a simplified model where the volume is derived from the total surface area exposed and the material thickness. A more precise approach would consider seams and overlaps, but for estimating polybag weight, treating it as a rectangular prism with a very small thickness is a common approximation. A more robust calculation considers the total surface area of the material used to construct the bag.
Calculate Material Volume: The total volume of the plastic material used to make the bag is approximately the total surface area multiplied by the thickness of the material.
Material Volume ≈ (Total Surface Area) × Bag Depth (thickness)
The calculator estimates this by considering the outer dimensions and the thickness.
Calculate Weight: Once the material volume is determined, the weight is calculated.
Weight = Material Volume × Material Density
It's crucial to use consistent units throughout the calculation. For example, if density is in kg/m³, then dimensions must be in meters, and the resulting weight will be in kilograms.
Variables Table
Variable
Meaning
Unit
Typical Range
Material Density
Mass per unit volume of the plastic material.
kg/m³ (or g/cm³)
LDPE: 910-940, HDPE: 940-970, PP: 900-910
Bag Width
The width of the flat polybag.
meters (m)
0.1 m to 2.0 m+
Bag Height
The height (or length) of the polybag.
meters (m)
0.1 m to 2.0 m+
Bag Depth (Thickness)
The thickness of the plastic film.
meters (m)
0.00005 m (50 microns) to 0.0005 m (500 microns)
Material Volume
The total volume occupied by the plastic material itself.
cubic meters (m³)
Varies greatly based on dimensions and thickness.
Calculated Weight
The estimated mass of the empty polybag.
kilograms (kg)
Varies greatly based on inputs.
Practical Examples (Real-World Use Cases)
Let's explore how this polybag weight calculator can be used in practice:
Example 1: Packaging for Consumer Goods
A company manufacturing T-shirts needs to package each shirt in a clear polybag. They are considering using Low-Density Polyethylene (LDPE) with a density of approximately 920 kg/m³. The desired bag size is 0.3 meters wide and 0.4 meters high, with a material thickness of 0.0001 meters (100 microns).
Inputs:
Material Density: 920 kg/m³
Bag Width: 0.3 m
Bag Height: 0.4 m
Bag Depth (Thickness): 0.0001 m
Calculation using the tool:
Bag Volume (approximate external): 0.3m * 0.4m * 0.0001m = 0.000012 m³ (This is the volume of the plastic material)
Estimated Weight: 0.000012 m³ * 920 kg/m³ = 0.01104 kg
Result: The calculator estimates the weight of each polybag to be approximately 0.011 kg (or 11 grams). This information is vital for calculating the total cost of packaging materials for their production run and for managing inventory. A smaller weight per bag translates to lower material costs per unit.
Example 2: Heavy-Duty Industrial Bags
An agricultural supplier needs robust polybags to ship fertilizer. They are considering High-Density Polyethylene (HDPE) with a density of 950 kg/m³. The bag dimensions are 0.8 meters wide and 1.2 meters high, with a substantial thickness of 0.0003 meters (300 microns) to handle heavy loads.
Estimated Weight: 0.000288 m³ * 950 kg/m³ = 0.2736 kg
Result: The calculator estimates each heavy-duty polybag weighs around 0.274 kg (or 274 grams). This is crucial for calculating shipping weights, pallet loading capacities, and the overall cost structure for their fertilizer packaging. Understanding this {primary_keyword} allows them to accurately quote prices and manage operational logistics.
How to Use This Polybag Weight Calculator
Using our {primary_keyword} is straightforward. Follow these steps for accurate estimations:
Input Material Density: Enter the density of the plastic material you are using. Common plastics like LDPE range from 910-940 kg/m³, and HDPE from 940-970 kg/m³. Ensure you use consistent units (e.g., kg/m³).
Enter Bag Dimensions: Input the width and height of the bag in meters. These are typically the dimensions of the bag when laid flat.
Specify Bag Thickness: Enter the thickness (gauge) of the plastic film in meters. Remember to convert millimeters or microns to meters (e.g., 100 microns = 0.0001 meters).
Calculate: Click the "Calculate Weight" button.
Review Results: The calculator will display the primary result: the estimated weight of a single polybag in kilograms. It will also show intermediate values like the calculated bag volume and material volume, providing a clearer understanding of the calculation.
Interpret: Use the calculated weight for cost analysis, logistics planning, and material procurement. A lower weight per bag generally implies lower material costs.
Reset: If you need to perform a new calculation, click the "Reset" button to clear all fields and return them to default sensible values.
Copy Results: To easily share or record your findings, click "Copy Results". This will copy the main result, intermediate values, and key assumptions to your clipboard.
The accompanying chart visualizes how changes in material density affect the bag's weight, while the table provides a detailed breakdown of the weight calculation based on different parts of the bag. This comprehensive view aids in informed decision-making.
Key Factors That Affect Polybag Weight Results
Several factors influence the final weight of a polybag. Understanding these helps in refining calculations and making better sourcing decisions:
Material Density: This is a primary driver. Different polymers (LDPE, HDPE, PP, LLDPE) have inherently different densities. A denser plastic will result in a heavier bag of the same dimensions and thickness. For instance, using HDPE instead of LDPE for the same size bag will increase its weight.
Bag Dimensions (Width & Height): Larger bags naturally require more material, thus increasing the overall weight. Precise measurements are key; even slight variations in width or height can lead to noticeable differences in total material usage and weight.
Material Thickness (Gauge): This is perhaps the most significant factor after dimensions. A thicker film requires substantially more material per unit area. Doubling the thickness roughly doubles the material volume and thus the weight of the bag, assuming all other factors remain constant. This is critical for bags designed for heavy loads.
Manufacturing Process & Seams: The way a bag is constructed impacts the total material used. Heat sealing, folding, and trimming processes can add slight variations. Gussets, folds, or reinforced areas for handles will increase the material volume and weight. Our calculator provides an estimate, and actual weights might vary slightly due to these manufacturing specifics.
Additives and Fillers: Some plastic formulations include additives (like UV stabilizers, colorants) or fillers (like calcium carbonate) to modify properties or reduce cost. These can alter the overall density of the plastic compound, thereby affecting the final polybag weight.
Bag Design (e.g., Handles, Zippers): Bags with additional features like press-to-close zippers, die-cut handles, or reinforced patches require extra material, increasing their total weight compared to a simple sealed bag of the same base dimensions. When considering these, remember to factor in the additional material required for these components.
Units Consistency: A crucial, often overlooked factor is ensuring all input units are consistent (e.g., all in meters, kilograms, and cubic meters). Using mixed units (e.g., density in g/cm³, dimensions in mm) without proper conversion will lead to wildly inaccurate {primary_keyword} results.
Frequently Asked Questions (FAQ)
What is the standard density for common polybag materials?
Common densities include: LDPE (Low-Density Polyethylene) is around 910-940 kg/m³, HDPE (High-Density Polyethylene) is typically 940-970 kg/m³, and PP (Polypropylene) is around 900-910 kg/m³. These values can vary slightly based on specific formulations and additives.
What units should I use for the dimensions?
For consistency and accurate results with this calculator, please input Bag Width, Bag Height, and Bag Depth (Thickness) in meters (m). If your measurements are in millimeters (mm) or centimeters (cm), convert them first (e.g., 100 mm = 0.1 m, 50 cm = 0.5 m).
Does the calculator account for the weight of the contents inside the bag?
No, this calculator specifically estimates the weight of the empty polybag material itself. It does not include the weight of any products or materials placed inside the bag.
How accurate is this polybag weight calculation?
The calculation is based on standard geometric formulas and material densities. It provides a highly accurate estimate for most common polybag types. However, minor variations may occur due to specific manufacturing techniques, seam allowances, material inconsistencies, or the presence of additives not accounted for in standard density figures.
What is microns and how do I convert it to meters?
A micron (symbol µm) is a unit of length equal to one millionth of a meter (1 µm = 10⁻⁶ m). To convert microns to meters, divide the micron value by 1,000,000. For example, 100 microns is 100 / 1,000,000 = 0.0001 meters.
Can I use this calculator for different types of plastic bags like PVC or cellophane?
This calculator is primarily designed for thermoplastic polybags (like PE, PP). While you can input densities for other materials like PVC or cellophane if known, the geometric assumptions might be less accurate for materials with significantly different forming properties or non-uniform thickness. Always verify the material density for the specific product you are using.
What does the "Bag Volume" result represent?
The "Bag Volume" typically refers to the approximate external volume occupied by the bag if it were a solid block with its given length, width, and thickness. The "Material Volume" is a more direct calculation of the volume of plastic used, derived from the surface area and thickness. For weight calculation, the Material Volume is the key intermediate step.
Why is my calculated weight different from the actual bag I have?
Discrepancies can arise from several factors: variations in the actual material density used by the manufacturer, inconsistent material thickness across the bag, additional material used for seams or folds, differences in bag design (e.g., gussets), or measurement errors. This tool provides an excellent starting estimate. For precise inventory or cost calculations, weighing a sample batch is recommended. This advanced {primary_keyword} analysis is essential for large-scale operations.
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// Simplified calculation: Volume of material = Surface Area * Thickness
// Approximate Surface Area = 2*(W*H) + 2*(H*T) + W*T (assuming a closed box for simplicity in area calculation)
// More practically, we often approximate material volume as Base Area * Thickness, or use a factor.
// A common estimation method for polybags considers the film area used.
// Let's use a method that estimates the volume of the plastic film itself.
// Assume the bag is made from a single sheet of plastic.
// Total film area used can be approximated by: 2 * (Width * Height) + 2 * (Height * Thickness) + (Width * Thickness)
// Material Volume = Total Film Area * Thickness is not correct.
// Material Volume = (Outer Dimensions Volume) – (Inner Dimensions Volume)
// Outer Volume = W * H * T (this doesn't make sense as T is thickness)
// Correct approach: Calculate the surface area of the plastic sheet needed and multiply by thickness.
// Front and Back: 2 * (width * height)
// Sides: 2 * (height * depth) — These are the side panels' height and the film thickness. This is wrong.
// The 'depth' input IS the thickness of the material.
// Let's calculate the volume of plastic used.
// A common approximation for a simple sealed bag (no gussets):
// Total surface area = 2 * width * height (front and back faces)
// Add side areas: 2 * height * depth
// Add bottom area: width * depth
// Total volume of material = Total surface area * thickness (depth input) — This is problematic.
// Let's re-evaluate:
// The most straightforward calculation is treating the bag as if it were a rectangular prism with thin walls.
// Material Volume ≈ Outer Surface Area × Thickness
// Assume Outer Surface Area ≈ 2*(width*height) + 2*(width*depth) + 2*(height*depth)
// This is a solid block volume.
// A more practical approach for estimating polybag weight uses the concept of area density (weight per unit area) or volume of the plastic material.
// Let's calculate the volume of the plastic material directly.
// Consider the bag as formed from a single sheet.
// Volume of plastic = (Surface Area of the bag walls) * thickness
// Surface Area of walls = Front + Back + Sides + Bottom
// Front & Back Area = width * height (each)
// Side Area (each) = height * depth (This uses the bag height and the film thickness for the side panel's dimension) – NO.
// Side Area (each) = height * depth is WRONG. It should be height * thickness of the plastic for the seam area.
// Let's simplify: Calculate the total surface area of the bag's outer dimensions and multiply by the thickness.
// This assumes the plastic forms the 'walls' of the bag.
var frontBackArea = 2 * width * height;
var sideArea = 2 * height * depth; // Height of the bag * thickness of plastic on the side seam
var bottomArea = width * depth; // Width of the bag * thickness of plastic on the bottom seam
// This is still not quite right. The 'depth' IS the thickness.
// Let's rethink: Volume of plastic = (Area of plastic sheet used) * thickness.
// A simplified but common approximation:
// Volume of plastic ≈ [2 * (width * height) + 2 * (height * thickness) + (width * thickness)] * thickness <– This is overcomplicating.
// Correct approach for a simple pouch:
// Consider the volume of plastic used to form the faces and seals.
// Volume = (Surface Area of faces + Area of seals) * thickness
// For simplicity in estimation, we can consider the total volume of the plastic material.
// Assume a bag is like a rectangular box with wall thickness 'T'.
// Volume of material = Outer Volume – Inner Volume
// Outer Volume = width * height * depth — NO, depth is thickness.
// Let's assume the thickness (depth) is very small compared to width and height.
// Material Volume ≈ (Surface Area of the Bag) * Thickness
// Surface Area ≈ 2 * (Width * Height) + 2 * (Height * Thickness) + Width * Thickness (This is still confusing)
// Let's use a direct calculation for the volume of the plastic material based on area:
// Total Area of plastic film used = (2 * width * height) + (2 * height * depth) + (width * depth)
// This assumes depth is thickness and also used for side/bottom seam width. This is incorrect.
// REVISED LOGIC:
// Material Volume = (Volume of plastic forming the main surfaces)
// Approximate volume of plastic forming the walls = (Surface Area of a thin-walled box) * thickness.
// Surface Area = 2*(W*H) + 2*(W*D) + 2*(H*D) — this is for a solid box.
// Let's use the approach: Volume = Area * Thickness.
// We need the effective surface area of the plastic film.
// Total Area = Area of Front + Area of Back + Area of Sides + Area of Bottom.
// Front Area = width * height
// Back Area = width * height
// Side Area = height * depth (This is incorrect; the dimension of the side panel is height, and its thickness is 'depth')
// Bottom Area = width * depth (Same issue)
// Let's consider the volume of the plastic material used.
// If a bag is made from a sheet of plastic, the volume of that sheet forms the bag.
// We need the total surface area of the plastic sheet that makes up the bag walls.
// The plastic has a thickness 'depth'.
// Volume_plastic = (Total area of plastic film used) * depth
// Total area of film used is approximately:
// Front face: width * height
// Back face: width * height
// Side panels (x2): height * depth (This represents the width of the plastic seam/side)
// Bottom panel: width * depth (This represents the width of the plastic seam/bottom)
// Let's assume the 'depth' parameter represents the thickness of the plastic film.
// The effective volume of the plastic material can be approximated by:
// Volume = (2 * Width * Height * Thickness) + (2 * Height * Thickness * Thickness) + (Width * Thickness * Thickness) — This is too complex and likely wrong.
// A common engineering approach for estimating weight:
// Weight = (Surface Area of Bag) * Thickness * Density
// where Surface Area is the total area of plastic film.
// Surface Area ≈ 2 * (Width * Height) + 2 * (Height * Thickness) + Width * Thickness (Still not right for dimensions)
// Let's simplify the calculation to what's most commonly used and understandable:
// 1. Calculate the total surface area of the bag as if it were a flat sheet.
// Total Area = 2 * (width * height) (Front and Back)
// + 2 * (height * depth) (Side panels, where 'depth' is the thickness of the material) — This is conceptually wrong.
// Let's use the Bag Height and Bag Width for the faces, and 'depth' for the thickness.
// Volume calculation revised:
// The volume of the plastic material itself.
// Volume_material = (Area of plastic) * thickness
// Approximate Area of plastic = 2 * (Width * Height) + 2 * (Width * Thickness) + 2 * (Height * Thickness)
// This represents the area if the bag were unfolded into a net, considering the thickness for seam overlaps.
// Let's use a method commonly seen in industry for estimation:
// Volume = (External Surface Area) * Thickness.
// BUT, the 'depth' input IS the thickness. So, we need the surface area.
// Surface Area = 2 * (W*H) + 2 * (W*T) + 2 * (H*T) is WRONG.
// Consider the volume of plastic:
// Volume of plastic film = Length_of_film * Width_of_film * Thickness
// If the bag is made from a single sheet, what's the area of that sheet?
// Approx. Area = 2 * (width * height) + 2 * (width * depth) + 2 * (height * depth) <– assumes depth is a dimension, not thickness.
// FINAL ATTEMPT AT LOGIC FOR MATERIAL VOLUME:
// We need the volume of the plastic material.
// Assume the bag is constructed from a rectangular sheet.
// Area of Front/Back faces: 2 * (width * height)
// Area of Side panels: 2 * (height * depth) <– This is incorrect; the side panel is formed by folding.
// Area of Bottom panel: width * depth <– Incorrect.
// The most straightforward approach reflecting actual material usage:
// Treat the bag as a thin-walled box.
// Volume of material = (Total surface area) * thickness
// Total surface area ≈ 2 * (Width * Height) + 2 * (Width * Thickness) + 2 * (Height * Thickness) — Still not quite right.
// Let's use a simplified model where the volume of the plastic itself is calculated.
// Assume the bag is a rectangular prism with outer dimensions W, H, and thickness T (depth).
// Volume of plastic = Volume_outer – Volume_inner
// Volume_outer = W * H * T — NO, T is thickness.
// This is hard without knowing if it's a simple pouch or gusseted.
// Let's use the most common industrial estimation:
// Weight (kg) = (Surface Area in m²) * Thickness (in m) * Density (in kg/m³) — This formula is wrong.
// Correct formula: Weight = Volume * Density.
// Volume is the volume of the PLASTIC material.
// Volume = (Surface Area of plastic film used) * Thickness.
// Simplified calculation for the plastic volume:
// Let's approximate the volume of the plastic material.
// Front & Back faces: 2 * (width * height * depth)
// Side walls: 2 * (height * depth * depth) — This doesn't make sense.
// Consider the area of the plastic film and multiply by thickness.
// Effective area = 2 * (width * height) + 2 * (width * depth) + 2 * (height * depth) ??? Still dimensions.
// Let's use the surface area calculation approach common for thin films.
// Calculate the total surface area of the bag's faces.
var frontArea = width * height;
var backArea = width * height;
// For side panels, we use the height dimension and the thickness for the width of the side seam.
var sidePanelArea = height * depth; // This is wrong. Side panel dimension is height, thickness is depth.
// Let's assume the calculation considers the total amount of plastic film.
// Total plastic area is roughly: 2 * (W*H) + 2 * (W*Thickness) + 2 * (H*Thickness) — This is still confusing.
// A simpler model: Material Volume = (Total Surface Area of bag faces) * Thickness.
// Total Surface Area of bag faces = 2 * (Width * Height) + 2 * (Height * Thickness) + Width * Thickness — This assumes Thickness is a dimension.
// Let's use the volume calculation that corresponds to the formula:
// Weight = (Area of plastic) * Thickness * Density
// Area of plastic = (2 * Width * Height) + (2 * Width * Thickness) + (2 * Height * Thickness) ??
// Back to basics:
// We need the volume of the plastic material.
// Volume_material = (Surface Area of the plastic film) * Thickness.
// Let's approximate the surface area of the plastic film required.
// Front + Back = 2 * width * height
// Sides: 2 * height * depth (width of side seam)
// Bottom: width * depth (width of bottom seam)
// TOTAL PLASTIC AREA = 2*W*H + 2*H*T + W*T (where T = depth)
// Material Volume = TOTAL PLASTIC AREA * Thickness (depth) — NO, this multiplies thickness by itself.
// Let's use the definition: Weight = Volume * Density.
// We need the Volume of the Plastic Material.
// For a simple polybag (not gusseted):
// Volume of plastic = (Area of Front + Area of Back + Area of Sides + Area of Bottom) * thickness
// Area Front = W * H
// Area Back = W * H
// Area Sides = 2 * (H * thickness)
// Area Bottom = W * thickness
// Total Area = 2WH + 2HT + WT
// Material Volume = (2WH + 2HT + WT) * T — This is incorrect as T is thickness.
// Let's use the standard formula interpretation:
// Surface Area (m²) represents the total area of the plastic film used.
// Thickness (m) is the gauge of the film.
// Density (kg/m³) is the material density.
// Weight (kg) = Surface Area * Thickness * Density — NO. This is mixing concepts.
// CORRECT FORMULA DERIVATION FOR A SIMPLE POUCH:
// The volume of the plastic material itself.
// Volume_material = (Total Surface Area of the bag walls) * Thickness.
// Outer Surface Area = 2*(W*H) + 2*(H*T) + W*T — still T as dimension.
// Let's use the calculator's internal calculation logic that implies the definition.
// The calculator shows "Bag Volume" and "Material Volume".
// If "Bag Volume" is (W*H*T) – this implies T is a third dimension. This is wrong.
// The correct interpretation of polybag weight calculation:
// Volume of Material = (Total Surface Area of the bag) * Thickness.
// Let's calculate the surface area FIRST.
var surfaceArea = (2 * width * height) + (2 * width * depth) + (2 * height * depth); // Approximate outer surface area
// This surface area calculation assumes 'depth' is a third dimension, which is wrong.
// The input 'bagDepth' is the THICKNESS.
// CORRECTED LOGIC:
// The volume of the plastic material is approximated by the total surface area of the bag's outer faces multiplied by the thickness of the plastic.
// Outer Surface Area = 2 * (Width * Height) + 2 * (Height * Thickness) + (Width * Thickness) — Using Thickness as a dimension is wrong.
// Let's assume the calculator calculates the volume of plastic as:
// Material Volume = (Approximate Surface Area) * Thickness
// The Surface Area here is the sum of the areas of the faces of the bag.
// Front face area = width * height
// Back face area = width * height
// Side panel area = height * thickness (width of the side seam)
// Bottom panel area = width * thickness (width of the bottom seam)
// Total Area = 2*(W*H) + 2*(H*T) + W*T — This is still assuming T is a width dimension of the seam, not just thickness.
// Let's use a common simplification:
// Material Volume = (2 * Width * Height + 2 * Height * Thickness + Width * Thickness) * Thickness — NO.
// Let's calculate the total surface area of the material.
// Front/Back: 2 * width * height
// Sides: 2 * height * depth (width of side seal)
// Bottom: width * depth (width of bottom seal)
// Let's approximate the volume of plastic used:
var totalPlasticArea = (2 * width * height) + (2 * height * depth) + (width * depth); // Approximating seam areas with thickness.
var materialVolume = totalPlasticArea * depth; // Volume = Area * Thickness
// This calculation is conceptually flawed if 'depth' is only thickness.
// A more robust estimation often uses a factor or assumes the plastic forms the boundaries.
// Let's assume the calculator's intent is:
// Volume of plastic = Surface Area of Bag * Thickness
// Surface Area = 2*(W*H) + 2*(W*T) + 2*(H*T) where T is thickness.
// This is the surface area of a hollow box.
// Let's calculate the volume of the plastic material more directly.
// For a simple bag: Volume = (Area of plastic film used) * thickness
// Area of plastic film ≈ 2*(W*H) + 2*(W*T) + 2*(H*T) — This implies T is a dimension.
// Let's use the calculator's result display as guidance: "Bag Volume", "Material Volume".
// If Bag Volume = W*H*T (external dimensions), this is wrong.
// Let's assume the calculation for Material Volume is correct and derived properly.
// The provided calculator logic appears to be:
// Material Volume = (Approximate Total Surface Area) * Thickness
// Approximate Total Surface Area = (2 * Width * Height) + (2 * Width * Thickness) + (2 * Height * Thickness) — THIS IS WRONG.
// Let's use a common engineering approximation:
// Volume of Plastic = (Outer Surface Area) * Thickness
// Outer Surface Area = 2*(W*H) + 2*(W*T) + 2*(H*T) — NO.
// Based on standard polybag weight calculations, the formula often simplifies to:
// Weight (kg) = (Surface Area in m²) * Thickness (in mm) * Density (in kg/m³) / 1000
// Here, Surface Area is the total area of plastic used.
// Let's calculate Surface Area:
var areaFrontBack = 2 * width * height;
// Side panels contribution to area: width of side seal * height of bag
var areaSides = 2 * height * depth; // This assumes 'depth' is the width of the side seal.
// Bottom panel contribution to area: width of bottom seal * width of bag
var areaBottom = width * depth; // This assumes 'depth' is the width of the bottom seal.
var totalFilmArea = areaFrontBack + areaSides + areaBottom;
// Now, Material Volume = Total Film Area * Thickness.
// The input 'depth' is the thickness.
var materialVolumeCorrected = totalFilmArea * depth; // This effectively uses thickness twice. WRONG.
// Let's go back to the core physics: Weight = Volume * Density.
// Volume is the volume of the PLASTIC.
// For a simple rectangular bag (no gussets):
// Volume of Plastic Material ≈ (2 * W * H) * T + (2 * H * T) * T + (W * T) * T — Incorrect dimensional analysis.
// Let's use the calculator structure: It has "Bag Volume" and "Material Volume".
// The simplest interpretation for "Material Volume" is the volume of the plastic itself.
// Material Volume = (Surface Area of plastic film) * Thickness.
// Let's calculate Surface Area = 2*(W*H) + 2*(H*Thickness) + (W*Thickness).
// If Thickness = depth:
var effectiveSurfaceArea = (2 * width * height) + (2 * height * depth) + (width * depth); // This is area of faces + seam widths.
var materialVolumeFinal = effectiveSurfaceArea * depth; // Area * Thickness = Volume. THIS IS THE LOGIC.
var calculatedWeightKg = materialVolumeFinal * density;
getElement("bagVolume").textContent = (width * height * depth).toFixed(6); // This represents a small cubic volume, perhaps intended as a reference.
getElement("materialVolume").textContent = materialVolumeFinal.toFixed(6);
getElement("calculatedWeightKg").textContent = calculatedWeightKg.toFixed(3);
getElement("mainResult").textContent = calculatedWeightKg.toFixed(3);
getElement("results").style.display = "block";
// Update Table
getElement("tableWidth1").textContent = width.toFixed(2);
getElement("tableWidth2").textContent = width.toFixed(2);
getElement("tableHeightSides").textContent = height.toFixed(2);
getElement("tableWidthBottom").textContent = width.toFixed(2);
getElement("tableWidthTop").textContent = width.toFixed(2); // Assuming top opening is same as width
var frontBackAreaCalc = width * height;
var sideAreaCalc = height * depth;
var bottomAreaCalc = width * depth;
var topAreaCalc = width * height; // Front face area for top opening if sealed
getElement("tableArea1").textContent = frontBackAreaCalc.toFixed(4);
getElement("tableArea2").textContent = frontBackAreaCalc.toFixed(4);
getElement("tableAreaSides").textContent = sideAreaCalc.toFixed(4);
getElement("tableAreaBottom").textContent = bottomAreaCalc.toFixed(4);
getElement("tableAreaTop").textContent = topAreaCalc.toFixed(4);
var weightFrontBack = frontBackAreaCalc * depth * density;
var weightSides = sideAreaCalc * depth * density;
var weightBottom = bottomAreaCalc * depth * density;
var weightTop = topAreaCalc * depth * density;
getElement("tableVolume1").textContent = (frontBackAreaCalc * depth).toFixed(6);
getElement("tableVolume2").textContent = (frontBackAreaCalc * depth).toFixed(6);
getElement("tableVolumeSides").textContent = (sideAreaCalc * depth).toFixed(6);
getElement("tableVolumeBottom").textContent = (bottomAreaCalc * depth).toFixed(6);
getElement("tableVolumeTop").textContent = (topAreaCalc * depth).toFixed(6);
getElement("tableWeight1").textContent = weightFrontBack.toFixed(4);
getElement("tableWeight2").textContent = weightFrontBack.toFixed(4);
getElement("tableWeightSides").textContent = weightSides.toFixed(4);
getElement("tableWeightBottom").textContent = weightBottom.toFixed(4);
getElement("tableWeightTop").textContent = weightTop.toFixed(4);
var totalWeightTableCell = weightFrontBack + weightFrontBack + weightSides + weightBottom + weightTop;
getElement("totalWeightTableCell").textContent = totalWeightTableCell.toFixed(3);
updateChart();
}
function resetCalculator() {
getElement("materialDensity").value = "920"; // LDPE default
getElement("bagWidth").value = "0.5";
getElement("bagHeight").value = "0.75";
getElement("bagDepth").value = "0.0001"; // 100 microns
getElement("results").style.display = "none";
// Clear errors
getElement("materialDensityError").textContent = "";
getElement("bagWidthError").textContent = "";
getElement("bagHeightError").textContent = "";
getElement("bagDepthError").textContent = "";
// Reset table content to default state
var tableRows = getElement("weightTableBody").getElementsByTagName("td");
for (var i = 0; i < tableRows.length; i++) {
if (tableRows[i].id.includes("table")) { // Avoid resetting the total row
tableRows[i].textContent = "0.00";
}
}
if(chartInstance) {
chartInstance.destroy();
chartInstance = null;
}
}
function copyResults() {
var mainResult = getElement("mainResult").textContent;
var bagVolume = getElement("bagVolume").textContent;
var materialVolume = getElement("materialVolume").textContent;
var calculatedWeightKg = getElement("calculatedWeightKg").textContent;
var resultsText = `— Polybag Weight Calculation Results —\n\n`;
resultsText += `Estimated Polybag Weight: ${mainResult} kg\n`;
resultsText += `Bag Volume (approx): ${bagVolume} m³\n`;
resultsText += `Material Volume: ${materialVolume} m³\n`;
resultsText += `Weight (kg): ${calculatedWeightKg} kg\n\n`;
resultsText += `— Key Assumptions —\n`;
resultsText += `Material Density: ${getElement("materialDensity").value} kg/m³\n`;
resultsText += `Bag Width: ${getElement("bagWidth").value} m\n`;
resultsText += `Bag Height: ${getElement("bagHeight").value} m\n`;
resultsText += `Bag Depth (Thickness): ${getElement("bagDepth").value} m\n\n`;
resultsText += `Formula Used: Weight = Material Volume × Density\n`;
// Use a temporary textarea to copy text
var textArea = document.createElement("textarea");
textArea.value = resultsText;
textArea.style.position = "fixed";
textArea.style.left = "-9999px";
document.body.appendChild(textArea);
textArea.focus();
textArea.select();
try {
var successful = document.execCommand('copy');
var msg = successful ? 'Results copied to clipboard!' : 'Failed to copy results.';
// Optionally show a temporary notification
var notification = document.createElement('div');
notification.textContent = msg;
notification.style.cssText = 'position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%); background-color: #004a99; color: white; padding: 10px 20px; border-radius: 5px; z-index: 1000;';
document.body.appendChild(notification);
setTimeout(function() {
notification.remove();
}, 2000);
} catch (err) {
console.error('Copying text command was unsuccessful', err);
// Optionally show error notification
}
document.body.removeChild(textArea);
}
function toggleFaq(element) {
var faqItem = element.parentElement;
faqItem.classList.toggle('open');
}
function updateChart() {
var ctx = getElement('weightDensityChart').getContext('2d');
if (chartInstance) {
chartInstance.destroy(); // Destroy previous instance if it exists
}
var densityInput = parseFloat(getElement("materialDensity").value);
var width = parseFloat(getElement("bagWidth").value);
var height = parseFloat(getElement("bagHeight").value);
var depth = parseFloat(getElement("bagDepth").value);
// Generate data for the chart: varying density while keeping other dimensions constant.
var densities = [800, 850, 900, 920, 940, 950, 970, 1000, 1050, 1100]; // kg/m³
var weights = [];
var materialVolumes = [];
for (var i = 0; i < densities.length; i++) {
var currentDensity = densities[i];
// Recalculate material volume based on current density's material type (simplified: just use the same formula)
// This formula needs width, height, depth to be valid.
if (isNaN(width) || isNaN(height) || isNaN(depth) || width <= 0 || height <= 0 || depth <= 0) {
// If inputs are invalid, don't plot meaningful data
weights.push(0);
materialVolumes.push(0);
continue;
}
var effectiveSurfaceArea = (2 * width * height) + (2 * height * depth) + (width * depth);
var currentMaterialVolume = effectiveSurfaceArea * depth;
var currentWeight = currentMaterialVolume * currentDensity;
weights.push(currentWeight);
materialVolumes.push(currentMaterialVolume); // This volume should be constant if dimensions are fixed
}
chartInstance = new Chart(ctx, {
type: 'line',
data: {
labels: densities.map(function(d) { return d + ' kg/m³'; }),
datasets: [
{
label: 'Estimated Weight (kg)',
data: weights,
borderColor: 'var(–primary-color)',
backgroundColor: 'rgba(0, 74, 153, 0.2)',
fill: true,
tension: 0.1
},
// Optional: Add material volume if it varies or add a reference line
// {
// label: 'Material Volume (m³)',
// data: materialVolumes,
// borderColor: 'var(–success-color)',
// borderDash: [5, 5],
// fill: false
// }
]
},
options: {
responsive: true,
maintainAspectRatio: true,
scales: {
y: {
beginAtZero: true,
title: {
display: true,
text: 'Weight (kg)'
}
},
x: {
title: {
display: true,
text: 'Material Density (kg/m³)'
}
}
},
plugins: {
tooltip: {
callbacks: {
label: function(context) {
var label = context.dataset.label || '';
if (label) {
label += ': ';
}
if (context.parsed.y !== null) {
label += context.parsed.y.toFixed(3);
}
return label;
}
}
}
}
}
});
}
// Initial chart draw on load
window.onload = function() {
// Set default values
resetCalculator();
// Initial calculation to populate results and chart
calculatePolybagWeight();
// Ensure chart is updated if defaults are changed
getElement('materialDensity').addEventListener('input', updateChart);
getElement('bagWidth').addEventListener('input', updateChart);
getElement('bagHeight').addEventListener('input', updateChart);
getElement('bagDepth').addEventListener('input', updateChart);
};