Estimating rebar weight comes down to one famous shortcut: kg/m = d²/162, where d is the bar diameter in millimetres. Square the diameter, divide by 162, and you have the weight of one metre of that bar. Multiply by the total cutting length — length per bar times the number of bars — and you have the total steel weight to order or cost. The rule is just the steel density 7850 kg/m³ wrapped into a single number, which is why it appears on every bar bending schedule.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: steel density 7850 kg/m³ and the d²/162 unit-weight rule.
The rebar weight equations
The factor of 162 packages the steel density and the area formula πd²/4 into one constant, so you only have to square the diameter and divide. For total project steel, compute the unit weight for each bar size, multiply by that size's total length, and sum — the standard bar bending schedule method. The result is the theoretical weight; mill tolerances mean delivered bars can differ by a small percentage.
Worked example — a batch of bars
Scenario: You need ten 12 mm bars, each 6 metres long. What is the total steel weight?
The batch weighs about 53.3 kg, or 0.053 tonnes. Switch to 16 mm bars of the same length and quantity and the weight jumps to 1.58 × 60 = 94.8 kg — nearly double, because weight grows with the square of diameter. That square relationship is worth remembering: stepping up one common bar size adds far more steel (and cost) than the small change in diameter suggests.
Frequently Asked Questions
kg/m = d²/162 (d in mm). 12 mm → 144/162 = 0.889 kg/m. Total = unit weight × total length.
Steel density 7850 kg/m³ × area πd²/4 gives kg/m = 0.006165·d²; 1/0.006165 ≈ 162.
16²/162 ≈ 1.58 kg/m, so a 12 m bar ≈ 18.96 kg.
Unit weight × total length per size, summed across sizes — a bar bending schedule.
No — it's metric (mm → kg/m). Imperial bars (#4, #5) use published lb/ft values.