Steel Bar Weight Calculator in KG
Professional engineering tool for accurate reinforcement bar (rebar) weight estimation.
6 mm
8 mm
10 mm
12 mm
16 mm
20 mm
25 mm
32 mm
40 mm
50 mm
Select standard rebar size used in construction.
Standard full length bars are usually 12m.
Please enter a valid positive length.
Total number of bars required.
Please enter a valid positive quantity.
Total Steel Weight
106.67 kg
Unit Weight (per meter)
0.89 kg/m
Single Bar Weight (Full Length)
10.67 kg
Total Weight in Metric Tons
0.11 MT
Calculated using standard engineering formula: Weight = (D² / 162) × L
| Diameter (mm) | Unit Weight (kg/m) | Weight for Current Length (12m) | Total for Qty (100) |
|---|
What is a Steel Bar Weight Calculator in KG?
A steel bar weight calculator in kg is an essential digital tool used by civil engineers, construction site managers, and quantity surveyors to estimate the mass of reinforcement bars (rebars) required for a project. In construction, steel is typically purchased by weight (metric tons or kilograms) rather than by length. However, engineering drawings specify steel in terms of length and diameter.
This discrepancy makes accurate conversion critical. Whether you are calculating material for a small slab or a high-rise foundation, knowing the exact steel bar weight in kg helps in procurement, logistics planning, and structural load estimation. Incorrect calculations can lead to significant budget overruns or structural hazards.
Common misconceptions include assuming all steel grades have different densities that affect weight significantly. In reality, for standard construction estimation, the density of mild steel and TMT bars is universally accepted as approximately 7850 kg/m³, allowing for a standardized formula widely used across the industry.
Steel Bar Weight Formula and Mathematical Explanation
The core logic behind any steel bar weight calculator in kg is derived from the volume of a cylinder multiplied by the density of steel. However, for site ease, a simplified derivation is used.
The Derivation
1. Volume = Cross Section Area × Length
2. Area = (π × D²) / 4 (where D is diameter)
3. Density of Steel = 7850 kg/m³
By converting diameter from millimeters to meters and simplifying the constants, we arrive at the industry-standard thumb rule:
W = (D² / 162) × L
Where:
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| W | Total Weight | Kilograms (kg) | – |
| D | Diameter of Bar | Millimeters (mm) | 6mm – 50mm |
| L | Length of Bar | Meters (m) | 1m – 12m |
| 162 | Constant | Derived Factor | Constant |
Practical Examples (Real-World Use Cases)
Example 1: Residential Column Reinforcement
A contractor needs to order steel for 10 concrete columns. Each column requires 8 bars of 16mm diameter. Each bar is cut to a height of 3 meters.
- Input D: 16 mm
- Input L: 3 meters
- Input Quantity: 80 bars (10 cols × 8 bars)
- Calculation: Unit weight = (16 × 16) / 162 = 1.58 kg/m.
- Total Weight: 1.58 kg/m × 3m × 80 = 379.2 kg.
Financial Implication: At a market rate of $0.80 per kg, the material cost is approx $303.36.
Example 2: Slab Foundation (Raft)
A large foundation requires 12mm bars. The total running length calculated from the drawing is 2,500 meters.
- Input D: 12 mm
- Input L: 1 meter (for unit rate) or 2500 total length
- Calculation: Unit weight = (12 × 12) / 162 = 0.888 kg/m.
- Total Weight: 0.888 × 2500 = 2,220 kg (or 2.22 Metric Tons).
How to Use This Steel Bar Weight Calculator
- Select Diameter: Choose the diameter of the steel bar from the dropdown menu (e.g., 12mm, 16mm). These match standard market sizes.
- Enter Length: Input the length of a single bar in meters. Standard factory length is usually 12 meters, but cut pieces can be any length.
- Enter Quantity: Input the total number of bars required.
- Review Results: The tool instantly displays the unit weight (kg per meter), the weight of one specific bar, and the total weight for the entire quantity.
- Analyze the Chart: Use the chart to visualize how the weight accumulates over length compared to a heavier bar size.
Key Factors That Affect Steel Bar Weight Results
While the formula D²/162 is standard, several factors can influence the final steel bar weight in kg in a real-world scenario.
- Rolling Margin (Tolerance): Steel manufacturing is not perfect. Standards allow for a deviation (rolling margin) of ±3% to ±5% in weight. Actual delivered weight may differ slightly from theoretical weight.
- Steel Density Variations: While 7850 kg/m³ is standard for carbon steel, alloy steels or stainless steel rebars have slightly different densities, affecting the weight by 1-2%.
- Corrosion and Rust: Older bars stored outside may accumulate rust. While rust increases volume slightly, severe corrosion reduces the effective steel diameter, reducing the structural weight.
- Coating Weight: Epoxy-coated rebars (green bars) have an added layer of material. While lightweight, in massive quantities, the coating adds to the net weight.
- Length Wastage: Standard bars come in 12m lengths. If you need 3.5m pieces, cutting often results in scrap. This "wastage factor" (usually 3-5%) must be added to your calculated weight for accurate procurement.
- Lapping Length: In long spans, bars are overlapped (lapped) to maintain continuity. This overlap adds 40-50 times the diameter (50D) to the length, significantly increasing total steel weight.
Frequently Asked Questions (FAQ)
What is the standard formula for steel weight?
The universally accepted formula for construction sites is (D² / 162) × L, where D is diameter in mm and L is length in meters.
Why is 162 used in the formula?
The constant 162 is derived from the density of steel (7850 kg/m³) and mathematical constants. It simplifies the calculation so you don't need to calculate volume and density manually every time.
Does this calculator work for TMT bars?
Yes. TMT (Thermo-Mechanically Treated) bars are made of mild steel. The density remains ~7850 kg/m³, so the steel bar weight calculator in kg is perfectly accurate for TMT bars.
How do I convert the result to Tonnes?
Divide the result in kilograms by 1,000. For example, 2,500 kg equals 2.5 Metric Tons. Our calculator displays this automatically.
Is the calculated weight the same as the billing weight?
Not always. Suppliers often bill based on actual weighbridge weight. Theoretical weight (calculated here) is used for estimation, but rolling margins can cause a ±5% difference in billing.
What is the weight of a 12mm rod of 12 meters?
Using the formula: (12×12)/162 = 0.888 kg/m. Multiplied by 12m, the total weight is approximately 10.66 kg.
Can I calculate square bars with this tool?
No. This calculator is specifically for round reinforcement bars. Square bars require a different formula: Weight = Volume × Density, where Volume = Width × Height × Length.
How does length affect the cost?
Steel is sold by weight. However, buying non-standard lengths may incur cutting charges. It is usually most cost-effective to buy standard 12m bars and cut them on-site to minimize unit costs.
Related Tools and Internal Resources
Expand your construction estimation toolkit with these related resources:
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