Professional Engineering & Cost Estimation Calculator
Steel Weight & Cost Calculator
Calculate the theoretical weight and estimated cost of reinforcement steel bars.
Metric (mm, meters, kg)
Imperial (inches, feet, lbs)
Common sizes: 8, 10, 12, 16, 20, 25, 32 mm
Please enter a valid positive diameter.
Standard length is often 12 meters.
Please enter a valid positive length.
Total number of bars in the bundle.
Quantity must be at least 1.
Enter the current market price per kg or lb.
Total Weight
0.00 kg
Weight per Meter/Foot0.00 kg/m
Weight per Single Bar0.00 kg
Estimated Total Cost0.00
Formula Used: Weight = (D² / 162) × L
Weight Analysis Chart
Standard Weight Reference Table
Diameter (mm)
Weight (kg/m)
Weight per 12m Bar (kg)
8 mm
0.395
4.74
10 mm
0.617
7.40
12 mm
0.888
10.66
16 mm
1.580
18.96
20 mm
2.470
29.64
25 mm
3.850
46.20
32 mm
6.310
75.72
Standard theoretical weights based on density 7850 kg/m³.
What is the "How to Calculate Weight of Steel Bar Formula"?
The phrase how to calculate weight of steel bar formula refers to the standard engineering method used to determine the theoretical mass of reinforcement steel (rebar) without needing a physical scale. This calculation is critical for civil engineers, site supervisors, and quantity surveyors to estimate material costs, plan logistics, and ensure structural integrity.
Steel bars are sold by weight, not just length. Therefore, knowing the exact weight allows for accurate procurement and billing. While physical weighing is the most accurate method, the theoretical formula provides a fast, reliable estimate based on the steel's density and volume.
Common misconceptions include assuming all steel grades have different densities (most mild and ribbed steel is approximately the same) or that the length of the bar doesn't impact the unit weight calculation.
How to Calculate Weight of Steel Bar Formula: Mathematical Explanation
The derivation of the formula comes from the basic physics equation: Mass = Volume × Density.
The Metric Formula (D²/162)
For circular bars in millimeters and meters:
W = (D² / 162) × L
W = Total Weight (kg)
D = Diameter of the bar (mm)
L = Length of the bar (meters)
162 = A derived constant (approximate)
Derivation of the Constant 162
The density of steel is approximately 7850 kg/m³. To find the weight per meter of a round bar:
Area of circle = π × r² = π × (D/2)² = (π × D²) / 4
Since D is usually in mm, we convert to meters: D/1000.
Calculation: Weight per meter = 16² / 162 = 256 / 162 = 1.58 kg/m.
Total Weight: 1.58 kg/m × 3m × 80 bars = 379.2 kg.
Financial Interpretation: If steel costs $0.90 per kg, the estimated material cost is $341.28.
Example 2: Slab Construction (Imperial Units)
A project requires #4 rebar (0.5 inches) for a slab. The total length required is 500 feet.
Input: Diameter = 0.5 inches, Length = 500 feet.
Formula (Imperial): Weight (lbs) = (D² × 2.67) × L (approx) or standard tables.
Calculation: #4 bar is 0.668 lbs/ft.
Total Weight: 0.668 × 500 = 334 lbs.
How to Use This Calculator
Follow these steps to effectively use the tool above for how to calculate weight of steel bar formula:
Select Unit System: Choose between Metric (mm/kg) or Imperial (inches/lbs) based on your project drawings.
Enter Diameter: Input the thickness of the rod. For metric, use integers like 8, 10, 12.
Enter Length: Input the total length of a single bar. Standard factory lengths are often 12m or 40ft.
Enter Quantity: If you are calculating for a bundle or a specific structural element, enter the count.
Enter Price (Optional): To get a financial estimate, input the current market rate per unit of weight.
Review Results: The calculator provides the unit weight (efficiency check) and total weight (procurement check).
Key Factors That Affect Steel Weight Results
When applying how to calculate weight of steel bar formula, consider these financial and physical factors:
Rolling Tolerance: Manufacturers have a margin of error. Actual weight may vary by ±3% to ±5% from the theoretical weight.
Corrosion (Rust): Heavily rusted bars lose mass, while surface rust might slightly increase weight readings on a scale due to oxidation layers, though the structural steel mass decreases.
Steel Grade: While density is generally constant, specific alloys or stainless steel variants may have slight density differences (e.g., 7900 kg/m³ vs 7850 kg/m³).
Coating Weight: Epoxy-coated or galvanized bars will weigh slightly more than black steel due to the added protective layer.
Wastage & Lapping: The formula calculates net weight. In finance estimation, you must add 5-10% for cutting wastage and lap lengths (overlapping bars).
Market Price Volatility: The calculated weight is constant, but the financial value fluctuates daily based on global raw material costs.
Frequently Asked Questions (FAQ)
Why is 162 used in the formula?
The number 162 is a simplified constant derived from the density of steel (7850 kg/m³) and the conversion of millimeters to meters in the volume formula. The precise number is 162.28, but 162 is the industry standard for quick calculation.
Does this formula work for square bars?
No. This specific formula (D²/162) is for circular cross-sections only. For square bars, the formula is Volume × Density, where Volume = Side² × Length.
How accurate is the theoretical weight?
It is generally accurate within 95-98%. However, for billing purposes, the actual weighbridge weight is usually the final authority.
Can I calculate the weight of TMT bars with this?
Yes, TMT (Thermo-Mechanically Treated) bars are standard reinforcement steel. The ribs on the surface are accounted for in the nominal diameter standards.
What is the density of steel in lbs/ft³?
The density of steel in imperial units is approximately 490 lbs/ft³.
How do I calculate cost from weight?
Once you have the total weight (e.g., in kg), multiply it by the current supplier price per kg. Don't forget to add tax and delivery fees.
Is 12m the only standard length?
12 meters is the most common international standard for transport logistics (fitting in 40ft containers), but 6m and custom lengths are also available.
Why is my actual bundle weight different from the calculation?
This is likely due to "rolling margin." Standards allow a deviation. If the bars are slightly oversized (over-tolerance), they will weigh more than the formula predicts.
Related Tools and Internal Resources
Enhance your construction finance and estimation toolkit with these related resources:
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calculateSteel();
};
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var lLabel = document.getElementById('lengthLabel');
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table.innerHTML = '
Diameter (mm)
Weight (kg/m)
Weight per 12m Bar (kg)
' +
'' +
'
8 mm
0.395
4.74
' +
'
10 mm
0.617
7.40
' +
'
12 mm
0.888
10.66
' +
'
16 mm
1.580
18.96
' +
'
20 mm
2.470
29.64
' +
'
25 mm
3.850
46.20
' +
'
32 mm
6.310
75.72
' +
'' +
'
Standard theoretical weights based on density 7850 kg/m³.
';
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// Update Table Headers for Imperial
table.innerHTML = '
Size (#)
Diameter (in)
Weight (lb/ft)
' +
'' +
'
#3
0.375
0.376
' +
'
#4
0.500
0.668
' +
'
#5
0.625
1.043
' +
'
#6
0.750
1.502
' +
'
#7
0.875
2.044
' +
'
#8
1.000
2.670
' +
'' +
'
Standard ASTM weights.
';
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var length = parseFloat(document.getElementById('length').value);
var quantity = parseFloat(document.getElementById('quantity').value);
var price = parseFloat(document.getElementById('price').value);
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// Formula: D^2 * 2.67 for inches to lbs/ft approx, or more precise calculation
// Density of steel ~ 490 lbs/ft3
// Area (sq ft) = (PI * (D/24)^2)
// Weight = Area * 490
// Simplified: D(in)^2 * 3.4 (approx)
// Standard engineering approx: Weight (lb/ft) = 2.67 * D(in)^2 is often cited but let's use the standard ASTM calculation logic
// Weight (lb/ft) = (Diameter in inches)² * 3.403 is physically derived, but standard tables differ slightly.
// Let's use: Weight = (D_in)^2 * 3.4
weightPerUnit = (diameter * diameter) * 3.4;
unitLabel = "lb/ft";
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document.getElementById('formulaDisplay').innerHTML = "Formula Used: Weight (lbs) ≈ (" + diameter + "² × 3.4) × " + length;
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var cost = document.getElementById('totalCost').innerText;
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ctx.clearRect(0, 0, canvas.width, canvas.height);
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var labels = ["Single Bar", "Total Bundle"];
var colors = ["#6c757d", "#004a99"];
// Scale
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ctx.fillRect(x, y, barWidth, barHeight);
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ctx.font = "bold 14px sans-serif";
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ctx.fillText(data[i].toFixed(1) + " " + unit, x + barWidth/2, y – 10);
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