How to Calculate Surface Area
Easily calculate the surface area of common geometric shapes with our comprehensive guide and interactive tool.
Surface Area Calculator
Cube
Rectangular Prism
Cylinder
Sphere
Cone
Triangular Prism
Choose the geometric shape for calculation.
Surface Area Calculation Results
What is Surface Area?
Surface area is a fundamental concept in geometry that quantifies the total area of the outer surfaces of a three-dimensional object. Imagine you could unfold a 3D shape and lay it flat; the surface area is the sum of the areas of all those flat pieces. It's a crucial measurement used across various fields, from engineering and manufacturing to packaging and even biology.
Who Should Use It: Anyone working with 3D objects needs to understand surface area. This includes students learning geometry, architects designing buildings, engineers calculating material needs for products, artists creating sculptures, and even homeowners estimating paint or wallpaper quantities. Understanding how to calculate surface area helps in determining material costs, heat transfer, fluid dynamics, and the overall physical properties of an object.
Common Misconceptions: A frequent misunderstanding is confusing surface area with volume. Volume measures the space an object occupies, while surface area measures its exterior. Another misconception is that all shapes have a simple, single formula; in reality, the complexity of the formula depends heavily on the shape's geometry. For irregular shapes, calculating surface area can become significantly more complex, often requiring calculus or approximation methods.
Surface Area Formula and Mathematical Explanation
The method to calculate surface area varies significantly depending on the geometric shape. Below, we break down the general approach and provide specific formulas for common shapes.
General Approach
The core principle is to identify all the distinct faces or surfaces of the 3D object, calculate the area of each individual surface, and then sum these areas together. For shapes with symmetry, like cubes or spheres, this process is simplified.
Formulas for Common Shapes
Here are the formulas for the shapes supported by our calculator:
Cube
A cube has 6 identical square faces. If 's' is the length of one side:
Formula: SA = 6s²
Rectangular Prism (Cuboid)
A rectangular prism has 6 rectangular faces. If 'l' is length, 'w' is width, and 'h' is height:
Formula: SA = 2(lw + lh + wh)
Cylinder
A cylinder has two circular bases and a curved lateral surface. If 'r' is the radius of the base and 'h' is the height:
Formula: SA = 2πr² + 2πrh
Sphere
A sphere is a perfectly round object. If 'r' is the radius:
Formula: SA = 4πr²
Cone
A cone has a circular base and a curved lateral surface. If 'r' is the radius of the base and 'l' is the slant height (the distance from the apex to a point on the edge of the base):
Formula: SA = πr² + πrl
Note: If only the height 'h' is given, the slant height 'l' can be found using the Pythagorean theorem: l = √(r² + h²).
Triangular Prism
A triangular prism has two triangular bases and three rectangular sides. If 'A_base' is the area of the triangular base, 'P_base' is the perimeter of the triangular base, and 'h' is the height (length) of the prism:
Formula: SA = 2 * A_base + P_base * h
Note: For a right triangular prism where the base is a right triangle with legs 'a' and 'b', and hypotenuse 'c', A_base = 0.5ab and P_base = a + b + c.
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| s | Side length of a cube | Length units (e.g., meters, feet) | > 0 |
| l, w, h | Length, Width, Height | Length units (e.g., meters, feet) | > 0 |
| r | Radius of a circle/sphere/cone base | Length units (e.g., meters, feet) | > 0 |
| h (cylinder/prism) | Height of cylinder or prism | Length units (e.g., meters, feet) | > 0 |
| l (cone) | Slant height of a cone | Length units (e.g., meters, feet) | > 0 |
| A_base | Area of the triangular base | Area units (e.g., m², ft²) | > 0 |
| P_base | Perimeter of the triangular base | Length units (e.g., meters, feet) | > 0 |
| π (Pi) | Mathematical constant | Unitless | Approx. 3.14159 |
Practical Examples (Real-World Use Cases)
Example 1: Painting a Room (Rectangular Prism)
Imagine you need to paint the four walls of a rectangular room. You want to calculate the total surface area of the walls to estimate how much paint you'll need. The room dimensions are: length = 5 meters, width = 4 meters, and height = 3 meters.
Inputs:
- Shape: Rectangular Prism
- Length (l): 5 m
- Width (w): 4 m
- Height (h): 3 m
Calculation:
We need the area of the four walls. This excludes the floor and ceiling. The formula for the lateral surface area of a rectangular prism is 2(lh + wh).
SA_walls = 2 * (5m * 3m + 4m * 3m)
SA_walls = 2 * (15 m² + 12 m²)
SA_walls = 2 * (27 m²)
SA_walls = 54 m²
Result: The total surface area of the walls to be painted is 54 square meters. This helps in determining the amount of paint required, considering the paint's coverage rate.
Example 2: Packaging a Cylindrical Product
A company is designing a cylindrical container for a new product. They need to determine the total surface area of the container to calculate the amount of material (like cardboard or plastic) needed for manufacturing.
Inputs:
- Shape: Cylinder
- Radius (r): 0.1 meters (10 cm)
- Height (h): 0.3 meters (30 cm)
Calculation:
The formula for the total surface area of a cylinder is SA = 2πr² + 2πrh.
SA = 2 * π * (0.1 m)² + 2 * π * (0.1 m) * (0.3 m)
SA = 2 * π * (0.01 m²) + 2 * π * (0.03 m²)
SA = 0.02π m² + 0.06π m²
SA = 0.08π m²
Using π ≈ 3.14159:
SA ≈ 0.08 * 3.14159 m²
SA ≈ 0.2513 m²
Result: The total surface area of the cylindrical container is approximately 0.2513 square meters. This figure is vital for material procurement and cost analysis in the manufacturing process. This calculation is essential for understanding material usage, which directly impacts production costs. For more insights into cost management, explore our cost analysis tools.
How to Use This Surface Area Calculator
Our interactive Surface Area Calculator is designed for simplicity and accuracy. Follow these steps to get your results:
- Select Shape: Use the dropdown menu to choose the geometric shape you want to calculate the surface area for (e.g., Cube, Cylinder, Sphere).
- Enter Dimensions: Based on the selected shape, relevant input fields will appear. Enter the required dimensions (like side length, radius, height) in the provided boxes. Ensure you use consistent units (e.g., all in meters, or all in feet).
- Calculate: Click the "Calculate Surface Area" button.
- View Results: The calculator will instantly display the total surface area as the primary result. It will also show key intermediate values used in the calculation and a clear explanation of the formula applied.
- Copy Results: If you need to save or share the results, click the "Copy Results" button. This will copy the main result, intermediate values, and assumptions to your clipboard.
- Reset: To start over with a new calculation, click the "Reset" button. This will clear the fields and restore default values.
How to Read Results: The main result is the total surface area of the object in square units (e.g., m², ft²). Intermediate values provide a breakdown of the calculation, showing the areas of different components (like bases or lateral surfaces). The formula explanation clarifies the mathematical steps taken.
Decision-Making Guidance: Use the calculated surface area to make informed decisions. For instance, if you're painting, use it to buy the right amount of paint. If you're manufacturing, use it to order the correct quantity of raw materials. Understanding surface area is key to efficient resource management and cost control. For related financial planning, consider our budgeting tools.
Key Factors That Affect Surface Area Results
While the formulas are precise, several factors influence the practical application and interpretation of surface area calculations:
- Dimensional Accuracy: The most critical factor is the accuracy of the input measurements (length, radius, height, etc.). Even small errors in measurement can lead to significant discrepancies in the calculated surface area, especially for complex shapes or large objects. Precise measurement tools are essential.
- Shape Complexity: Simple, regular shapes like cubes and spheres have straightforward formulas. However, irregular or composite shapes (objects made of multiple combined shapes) require breaking them down into simpler components or using advanced approximation techniques. The complexity directly impacts the calculation effort and potential for error.
- Units of Measurement: Consistency in units is paramount. If you measure length in meters and width in centimeters, the resulting area will be incorrect. Always ensure all input dimensions are in the same unit (e.g., all meters, all feet) before calculation. The final surface area will be in the corresponding square units (m², ft²).
- Slant Height vs. Perpendicular Height: For shapes like cones and pyramids, it's crucial to distinguish between perpendicular height (the distance from the apex to the center of the base) and slant height (the distance along the surface from the apex to the edge of the base). Using the wrong height in the formula will yield an incorrect surface area.
- Material Thickness and Overlap: When calculating surface area for manufacturing or construction, consider the thickness of materials and any necessary overlaps for joints or seams. These factors add to the total material required beyond the theoretical geometric surface area. For example, when calculating the amount of fabric for a tent (a composite shape), overlaps for stitching need to be accounted for.
- Holes, Cutouts, and Internal Surfaces: Standard surface area formulas typically apply to solid, closed objects. If an object has holes, cutouts, or internal surfaces (like the inside of a hollow pipe), these areas must be added or subtracted accordingly. Calculating the surface area of a hollow sphere, for instance, requires considering both the outer and inner surfaces.
- Rounding and Precision: Mathematical constants like Pi (π) are irrational numbers. Using a rounded value of π will affect the final result. The level of precision required depends on the application. For most practical purposes, using π ≈ 3.14159 is sufficient, but high-precision engineering might require more decimal places.
- Purpose of Calculation: The reason for calculating surface area influences how you interpret the result. Is it for estimating paint coverage, calculating heat loss, determining material costs, or understanding fluid dynamics? Each application might require adjustments or additional considerations beyond the basic geometric formula. For instance, calculating heat transfer involves factors like material emissivity, which are not part of the geometric surface area itself.
Frequently Asked Questions (FAQ)
- What is the difference between surface area and volume? Volume measures the three-dimensional space occupied by an object, while surface area measures the total area of its exterior surfaces. Think of volume as how much a container can hold, and surface area as how much material is needed to wrap it.
- Can I calculate the surface area of irregular shapes? Calculating the surface area of truly irregular shapes is complex. It often involves breaking the shape into simpler geometric components, using calculus (integration), or employing 3D scanning and modeling software for approximation. Our calculator handles standard geometric shapes.
- Why is surface area important in science and engineering? Surface area affects processes like heat transfer, chemical reactions, and fluid flow. For example, a larger surface area allows for faster heat dissipation or quicker dissolution of a substance. It's also critical in calculating material requirements for manufacturing and construction.
- Do I need to use specific units for measurements? Yes, you must use consistent units for all measurements entered into the calculator (e.g., all in centimeters, or all in inches). The resulting surface area will be in the corresponding square units (e.g., cm², in²).
- What is slant height, and when is it used? Slant height is the distance measured along the sloping surface of a cone or pyramid from the apex to the base edge. It's used in the surface area formulas for cones and pyramids, specifically for calculating the area of the lateral (sloping) surface.
- How does the calculator handle π (Pi)? The calculator uses a precise approximation of π (typically 3.14159 or higher) for calculations involving circles, spheres, cylinders, and cones to ensure accuracy.
- Can this calculator be used for hollow objects? The standard formulas calculate the surface area of solid objects. For hollow objects (like a pipe or a hollow sphere), you would typically calculate the outer surface area and the inner surface area separately and then sum them, depending on your needs. Our calculator provides the standard surface area for the given dimensions.
- What if my shape is a combination of different shapes? For composite shapes (e.g., a cylinder with a cone on top), you need to calculate the surface area of each component shape individually and then sum the relevant parts. You might need to subtract areas where the shapes join if they are internal. This calculator handles individual shapes. For complex composite shapes, consider consulting advanced geometry resources or software.
Related Tools and Internal Resources
- Volume Calculator Calculate the space occupied by 3D objects. Essential for understanding capacity and material fill.
- Perimeter Calculator Find the total length of the boundary of a 2D shape. Useful for fencing and framing projects.
- Area Calculator Calculate the 2D space enclosed by a shape. Fundamental for flooring, painting, and land measurement.
- BMI Calculator Assess body mass index based on height and weight. A health metric tool.
- Loan Amortization Calculator Understand loan repayment schedules and total interest paid over time. Key for financial planning.
- Cost Analysis Guide Learn how to break down project costs, including material estimation based on surface area calculations.
- Budgeting Tools Develop effective budgets for personal or business projects, incorporating material and labor costs.
Enter the length of one side of the cube.
`;
break;
case 'rectangular_prism':
html = `
Enter the length of the prism.
Enter the width of the prism.
Enter the height of the prism.
`;
break;
case 'cylinder':
html = `
Enter the radius of the cylinder's base.
Enter the height of the cylinder.
`;
break;
case 'sphere':
html = `
Enter the radius of the sphere.
`;
break;
case 'cone':
html = `
Enter the radius of the cone's base.
Enter the slant height of the cone.
Enter the perpendicular height if slant height is unknown. Slant height will be calculated.
`;
break;
case 'triangular_prism':
html = `
Enter the area of one triangular base.
Enter the perimeter of one triangular base.
Enter the height (length) of the prism.
`;
break;
}
inputSection.innerHTML = html;
// Trigger calculation if inputs are already filled (e.g., on page load with defaults)
// calculateSurfaceArea(); // Uncomment if you want immediate calculation on shape change
}
function validateInput(id, min = 0, max = Infinity) {
var input = document.getElementById(id);
var errorElement = document.getElementById(id + 'Error');
var value = parseFloat(input.value);
errorElement.style.display = 'none'; // Hide error by default
if (input.value.trim() === ") {
errorElement.textContent = 'This field cannot be empty.';
errorElement.style.display = 'block';
return false;
}
if (isNaN(value)) {
errorElement.textContent = 'Please enter a valid number.';
errorElement.style.display = 'block';
return false;
}
if (value max) {
errorElement.textContent = 'Value cannot exceed ' + max + '.';
errorElement.style.display = 'block';
return false;
}
return true;
}
function calculateSurfaceArea() {
var sa = 0;
var formula = ";
var intermediateValues = [];
var mainResultElement = document.querySelector('#result .main-result');
var intermediateValuesElement = document.querySelector('#result .intermediate-values');
var formulaExplanationElement = document.querySelector('#result .formula-explanation');
var resultDiv = document.getElementById('result');
resultDiv.style.display = 'none'; // Hide previous results
var isValid = true;
var inputs = {};
// Gather and validate inputs based on currentShape
switch (currentShape) {
case 'cube':
isValid = validateInput('cubeSide');
if (isValid) inputs.s = parseFloat(document.getElementById('cubeSide').value);
break;
case 'rectangular_prism':
isValid = validateInput('prismLength') &&
validateInput('prismWidth') &&
validateInput('prismHeight');
if (isValid) {
inputs.l = parseFloat(document.getElementById('prismLength').value);
inputs.w = parseFloat(document.getElementById('prismWidth').value);
inputs.h = parseFloat(document.getElementById('prismHeight').value);
}
break;
case 'cylinder':
isValid = validateInput('cylinderRadius') &&
validateInput('cylinderHeight');
if (isValid) {
inputs.r = parseFloat(document.getElementById('cylinderRadius').value);
inputs.h = parseFloat(document.getElementById('cylinderHeight').value);
}
break;
case 'sphere':
isValid = validateInput('sphereRadius');
if (isValid) inputs.r = parseFloat(document.getElementById('sphereRadius').value);
break;
case 'cone':
var coneRadiusInput = document.getElementById('coneRadius');
var coneSlantHeightInput = document.getElementById('coneSlantHeight');
var coneHeightInput = document.getElementById('coneHeight');
var rValid = validateInput('coneRadius');
var lValid = validateInput('coneSlantHeight');
var hValid = coneHeightInput.value.trim() === " || validateInput('coneHeight'); // Height is optional
if (rValid && lValid && hValid) {
inputs.r = parseFloat(coneRadiusInput.value);
inputs.l = parseFloat(coneSlantHeightInput.value);
var h = parseFloat(coneHeightInput.value);
// If slant height is provided, use it. If not, calculate it.
if (coneSlantHeightInput.value.trim() === ") {
if (h > 0) {
inputs.l = Math.sqrt(Math.pow(inputs.r, 2) + Math.pow(h, 2));
intermediateValues.push("Calculated Slant Height (l): " + inputs.l.toFixed(3));
} else {
isValid = false; // Need either slant height or height > 0
document.getElementById('coneHeightError').textContent = 'Enter slant height or a positive height.';
document.getElementById('coneHeightError').style.display = 'block';
}
}
} else {
isValid = false;
}
break;
case 'triangular_prism':
isValid = validateInput('triPrismBaseArea') &&
validateInput('triPrismPerimeter') &&
validateInput('triPrismHeight');
if (isValid) {
inputs.A_base = parseFloat(document.getElementById('triPrismBaseArea').value);
inputs.P_base = parseFloat(document.getElementById('triPrismPerimeter').value);
inputs.h = parseFloat(document.getElementById('triPrismHeight').value);
}
break;
}
if (!isValid) {
return; // Stop if validation failed
}
var pi = Math.PI;
// Perform calculation based on shape
switch (currentShape) {
case 'cube':
sa = 6 * Math.pow(inputs.s, 2);
formula = 'SA = 6 * s²';
intermediateValues.push("Area of one face: " + Math.pow(inputs.s, 2).toFixed(3));
break;
case 'rectangular_prism':
var lw = inputs.l * inputs.w;
var lh = inputs.l * inputs.h;
var wh = inputs.w * inputs.h;
sa = 2 * (lw + lh + wh);
formula = 'SA = 2(lw + lh + wh)';
intermediateValues.push("Area (lw): " + lw.toFixed(3));
intermediateValues.push("Area (lh): " + lh.toFixed(3));
intermediateValues.push("Area (wh): " + wh.toFixed(3));
break;
case 'cylinder':
var baseArea = pi * Math.pow(inputs.r, 2);
var lateralArea = 2 * pi * inputs.r * inputs.h;
sa = 2 * baseArea + lateralArea;
formula = 'SA = 2πr² + 2πrh';
intermediateValues.push("Area of one base (πr²): " + baseArea.toFixed(3));
intermediateValues.push("Lateral Surface Area (2πrh): " + lateralArea.toFixed(3));
break;
case 'sphere':
sa = 4 * pi * Math.pow(inputs.r, 2);
formula = 'SA = 4πr²';
intermediateValues.push("Area of one great circle (πr²): " + (pi * Math.pow(inputs.r, 2)).toFixed(3));
break;
case 'cone':
var baseArea = pi * Math.pow(inputs.r, 2);
var lateralArea = pi * inputs.r * inputs.l;
sa = baseArea + lateralArea;
formula = 'SA = πr² + πrl';
intermediateValues.push("Base Area (πr²): " + baseArea.toFixed(3));
intermediateValues.push("Lateral Surface Area (πrl): " + lateralArea.toFixed(3));
break;
case 'triangular_prism':
sa = 2 * inputs.A_base + inputs.P_base * inputs.h;
formula = 'SA = 2 * A_base + P_base * h';
intermediateValues.push("Area of two bases (2 * A_base): " + (2 * inputs.A_base).toFixed(3));
intermediateValues.push("Lateral Surface Area (P_base * h): " + (inputs.P_base * inputs.h).toFixed(3));
break;
}
// Display results
mainResultElement.textContent = sa.toFixed(3); // Display with 3 decimal places
intermediateValuesElement.innerHTML = ";
intermediateValues.forEach(function(val) {
var div = document.createElement('div');
div.textContent = val;
intermediateValuesElement.appendChild(div);
});
formulaExplanationElement.textContent = 'Formula Used: ' + formula + '. Calculates the total area of all external surfaces of the shape.';
resultDiv.style.display = 'block';
updateChart(); // Update the chart with new data
}
function resetCalculator() {
document.getElementById('shapeType').value = 'cube';
updateInputs(); // Re-render inputs for the default shape
document.getElementById('result').style.display = 'none';
// Optionally reset input values to defaults if needed
// Example: document.getElementById('cubeSide').value = ";
}
function copyResults() {
var resultDiv = document.getElementById('result');
if (resultDiv.style.display === 'none') {
alert('Please calculate the surface area first.');
return;
}
var mainResult = resultDiv.querySelector('.main-result').textContent;
var intermediateValuesHTML = resultDiv.querySelector('.intermediate-values').innerHTML;
var formulaExplanation = resultDiv.querySelector('.formula-explanation').textContent;
var textToCopy = "Surface Area Calculation Results:\n";
textToCopy += "———————————-\n";
textToCopy += "Total Surface Area: " + mainResult + "\n\n";
textToCopy += "Intermediate Values:\n";
// Simple parsing of intermediate values from HTML
var tempDiv = document.createElement('div');
tempDiv.innerHTML = intermediateValuesHTML;
tempDiv.querySelectorAll('div').forEach(function(div) {
textToCopy += "- " + div.textContent + "\n";
});
textToCopy += "\n" + formulaExplanation;
navigator.clipboard.writeText(textToCopy).then(function() {
// Success feedback (optional)
var copyButton = document.querySelector('.btn-copy');
var originalText = copyButton.textContent;
copyButton.textContent = 'Copied!';
setTimeout(function() {
copyButton.textContent = originalText;
}, 2000);
}).catch(function(err) {
console.error('Failed to copy text: ', err);
alert('Failed to copy results. Please copy manually.');
});
}
// Charting Logic
function updateChart() {
var canvas = document.getElementById('surfaceAreaChart');
var ctx = canvas.getContext('2d');
// Clear previous chart if it exists
if (chartInstance) {
chartInstance.destroy();
}
// Sample data generation – this should ideally be more dynamic or based on user input ranges
// For simplicity, let's create sample data based on the current shape and a range of inputs
var labels = [];
var dataSeries1 = []; // e.g., Surface Area
var dataSeries2 = []; // e.g., A hypothetical related metric or another dimension
var numPoints = 5; // Number of data points for the chart
switch (currentShape) {
case 'cube':
var baseSide = parseFloat(document.getElementById('cubeSide')?.value) || 5;
for (var i = 0; i 0) {
labels.push('s=' + side.toFixed(1));
dataSeries1.push(6 * Math.pow(side, 2));
dataSeries2.push(side); // Example: plotting side length itself
}
}
break;
case 'cylinder':
var baseRadius = parseFloat(document.getElementById('cylinderRadius')?.value) || 3;
var baseHeight = parseFloat(document.getElementById('cylinderHeight')?.value) || 7;
for (var i = 0; i 0 && height > 0) {
labels.push('r=' + radius.toFixed(1) + ', h=' + height.toFixed(1));
dataSeries1.push(2 * Math.PI * radius * radius + 2 * Math.PI * radius * height);
dataSeries2.push(radius * height); // Example: product of radius and height
}
}
break;
case 'sphere':
var baseRadius = parseFloat(document.getElementById('sphereRadius')?.value) || 5;
for (var i = 0; i 0) {
labels.push('r=' + radius.toFixed(1));
dataSeries1.push(4 * Math.PI * Math.pow(radius, 2));
dataSeries2.push(Math.pow(radius, 2)); // Example: plotting radius squared
}
}
break;
case 'rectangular_prism':
var baseLength = parseFloat(document.getElementById('prismLength')?.value) || 10;
var baseWidth = parseFloat(document.getElementById('prismWidth')?.value) || 6;
var baseHeight = parseFloat(document.getElementById('prismHeight')?.value) || 4;
for (var i = 0; i 0 && width > 0 && height > 0) {
labels.push('l=' + length.toFixed(1) + ', w=' + width.toFixed(1) + ', h=' + height.toFixed(1));
dataSeries1.push(2 * (length * width + length * height + width * height));
dataSeries2.push(length * width); // Example: base area
}
}
break;
// Add cases for cone and triangular prism if needed for chart data
default:
// Default or fallback data
labels.push('Default 1', 'Default 2', 'Default 3');
dataSeries1.push(10, 20, 30);
dataSeries2.push(5, 15, 25);
break;
}
// Ensure we have data before drawing
if (labels.length === 0) {
// Optionally display a message or draw a placeholder chart
canvas.style.display = 'none'; // Hide canvas if no data
return;
} else {
canvas.style.display = 'block'; // Show canvas
}
// Basic Charting using Canvas API (no external library)
// This is a simplified representation. A full charting library would be more robust.
// We'll simulate a bar chart for simplicity.
canvas.width = canvas.offsetWidth; // Set canvas size based on its container
canvas.height = canvas.offsetHeight;
var barWidth = (canvas.width / labels.length) * 0.6; // Width of each bar
var padding = canvas.width / labels.length * 0.2; // Padding between bars and groups
var maxValue = Math.max.apply(null, dataSeries1.concat(dataSeries2));
var chartHeight = canvas.height – 40; // Leave space for labels
ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear canvas
// Draw Y-axis label
ctx.fillStyle = '#333′;
ctx.font = '12px Arial';
ctx.textAlign = 'center';
ctx.fillText('Surface Area (Units²)', canvas.width / 2, 20);
// Draw bars
for (var i = 0; i < labels.length; i++) {
var x = padding + i * (barWidth + padding);
var barHeight1 = (dataSeries1[i] / maxValue) * chartHeight;
var barHeight2 = (dataSeries2[i] / maxValue) * chartHeight;
// Draw first series bar (e.g., Surface Area)
ctx.fillStyle = 'rgba(0, 74, 153, 0.7)'; // Primary color
ctx.fillRect(x, canvas.height – barHeight1 – 20, barWidth / 2, barHeight1);
// Draw second series bar (e.g., related metric)
ctx.fillStyle = 'rgba(40, 167, 69, 0.7)'; // Success color
ctx.fillRect(x + barWidth / 2, canvas.height – barHeight2 – 20, barWidth / 2, barHeight2);
// Draw X-axis label
ctx.fillStyle = '#333';
ctx.font = '10px Arial';
ctx.textAlign = 'center';
ctx.fillText(labels[i], x + barWidth / 2, canvas.height – 10);
}
// Add a simple legend
ctx.font = '12px Arial';
ctx.textAlign = 'left';
ctx.fillStyle = '#004a99';
ctx.fillRect(10, canvas.height – 35, 15, 10);
ctx.fillText('Surface Area', 30, canvas.height – 25);
ctx.fillStyle = '#28a745';
ctx.fillRect(10, canvas.height – 50, 15, 10);
ctx.fillText('Related Metric', 30, canvas.height – 40);
// Store chart instance for potential future updates/destruction
chartInstance = { destroy: function() { /* No-op for basic canvas */ } };
}
// Initial setup on page load
document.addEventListener('DOMContentLoaded', function() {
updateInputs(); // Load inputs for the default shape (cube)
// Optionally call calculateSurfaceArea() here if you want initial calculation
// calculateSurfaceArea();
updateChart(); // Draw initial chart
});