Reinforcement
Rebar weight per metre and total weight
- where
- mass per metre (kg/m)
- bar diameter (mm)
- total length (m)
- number of bars
- length of each bar (m)
- total mass (kg)
Explain this equation
Gives the weight of reinforcing bar per metre and in total, for ordering and checking deliveries.
A bar of diameter d has a cross-section of πd²/4 mm². Steel weighs 7850 kg/m³, so a metre of bar weighs πd² × 7850 / (4 × 10⁶) kg, which is d²/162 to a close approximation. Times the total length gives the weight.
Mass is area times length times density; the 162 bundles the constants.
Sense check: 12 mm bar is about 0.89 kg/m; 16 mm about 1.58 kg/m; ten 6 m lengths of 12 mm weigh about 53 kg.
Watch out: allow for laps, bends and hooks in the total length.
Works out the mass of steel reinforcing bar from its diameter and length, for ordering, scheduling and lifting.
Enter your values to see the result.
Good to know
d²/162 is the mass per metre of a round steel bar of density about 7850 kg/m³ with d in mm. It matches the BS 8666 table values to within about 0.1%: 8 mm 0.395, 10 mm 0.617, 12 mm 0.888, 16 mm 1.579, 20 mm 2.466, 25 mm 3.854 kg/m. Bars are supplied in stock lengths (commonly 6 m and 12 m); include bends and laps in the length.
Common mistake
Using the straight length on the drawing instead of the scheduled length, which leaves out laps, hooks and bends.
Limits
Nominal mass of plain round section. Ribbed bars are made to the same nominal mass per metre, within the rolling tolerance of BS 4449.
Sources
- BS 8666:2020 Scheduling, dimensioning, cutting and bending of steel reinforcement for concrete
- Designing Buildings Wiki, Rebar sizes (mass per metre: 6 mm 0.222, 8 mm 0.395, 10 mm 0.617, 12 mm 0.888, 16 mm 1.58, 20 mm 2.47, 25 mm 3.85, 32 mm 6.31 kg/m; BS 4449)
- CR Steel, Shape code / steel calculator sheet (BS 8666 bar masses; BS 4483 meshes A142 2.22, A193 3.02, A252 3.95, A393 6.16 kg/m²)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow BS 8500, BS EN 206, BS EN 752, Building Regulations Part H, manufacturers’ data and your engineer’s design. Structural concrete and foundations need a competent designer.