CostBuildrRebar Weight Formula and Chart
Knowing the weight of steel reinforcement bars is essential for material ordering, cost estimation, and structural calculations. The simple formula D²/162 gives you the weight per meter for any rebar size. This guide explains the formula and provides a ready reference chart.
The D²/162 Formula Explained
The formula W = D²/162 calculates the weight of one meter of steel rebar in kilograms, where D is the bar diameter in millimeters. It derives from the cross-sectional area formula (π/4 × D²) multiplied by steel density (7,850 kg/m³) and simplified to convenient units. For example, a 12 mm bar: W = 12²/162 = 144/162 = 0.889 kg/m.
This formula works for all standard deformed (ribbed) and plain round bars because the ribs add negligible weight. It assumes standard steel density of 7,850 kg/m³, which is accurate for all carbon steel reinforcement bars used in construction.
Complete Weight Reference Chart
Weight per meter for common sizes: 8 mm = 0.395 kg/m, 10 mm = 0.617 kg/m, 12 mm = 0.889 kg/m, 16 mm = 1.580 kg/m, 20 mm = 2.469 kg/m, 25 mm = 3.858 kg/m, 32 mm = 6.321 kg/m. To get weight per foot, multiply by 0.3048 (e.g., 10 mm bar = 0.188 kg/ft).
Steel is sold by weight (per ton or per kg), so converting your bar schedule into kilograms is essential for procurement. A standard bar length is 12 meters (40 ft). A single 12 m bar of 12 mm weighs 0.889 × 12 = 10.67 kg; of 10 mm weighs 0.617 × 12 = 7.4 kg.
Converting a Bar Schedule to Total Weight
List every bar by diameter and length from the structural drawing, multiply each bar's length by its weight per meter, then sum everything. For example, 50 bars of 12 mm × 6 m = 50 × 6 × 0.889 = 266.7 kg. Add 3–5% for overlaps, hooks, and cutting waste.
The standard overlap (lap) length is 40 times the bar diameter—e.g., 40 × 12 = 480 mm for 12 mm bars. Each overlap adds extra steel, and on a typical residential project with many short walls and columns, overlap steel can add 8–12% to the calculated straight-bar weight.
Questions fréquentes
What is the weight of a 10 mm steel bar per meter?
A 10 mm rebar weighs 0.617 kg per meter, calculated using D²/162 = 100/162 = 0.617. A standard 12-meter length weighs approximately 7.4 kg.
Does the D²/162 formula work for all types of steel?
Yes, it works for both deformed (ribbed) and plain round bars. It assumes standard steel density of 7,850 kg/m³, which is accurate for all carbon steel reinforcement bars.
How much waste should I add when ordering steel?
Add 3–5% for cutting waste and overlaps on a typical residential project. For complex designs with many different bar lengths, waste can reach 7–8%. Efficient bar scheduling can reduce waste to under 3%.