Bar weights and quantities
Rebar mass per metre and total weight (BS 4449 / BS 8666)
- where
- mass per metre of bar (kg/m)
- bar diameter (mm)
- total length of bar (m)
- number of bars
- length of each bar (m)
- total mass (kg)
- metres of bar per tonne (m/t)
Explain this equation
Works out how heavy a quantity of reinforcing bar is from its diameter and cut length. Use it to check a delivery note, price steel by the tonne or plan a lift.
m is the mass of one metre of bar. d² reflects the bar's cross-sectional area, which grows with the square of the diameter. Lt is the total length of all the bars, and M is the total mass. Lpt turns it round: how many metres of that size make one tonne.
A round steel bar has area πd²/4 and steel weighs about 7850 kg/m³. With d in mm, that works out to d² divided by about 162 kg per metre, which is the figure merchants and schedules use.
Sense check: 12 mm is about 0.89 kg/m, 16 mm about 1.58 kg/m and 25 mm about 3.85 kg/m. Doubling the diameter quadruples the weight, so one 20 mm bar weighs the same as four 10 mm bars.
Watch out: use the scheduled cutting length, including laps and bends, not the length shown on the drawing.
Works out the weight of reinforcing bar from its diameter and cut length, for checking deliveries, schedules, lifting and pricing by the tonne.
Enter your values to see the result.
Good to know
d²/162 is the mass of a round steel bar (density about 7850 kg/m³) in kg per metre with d in mm. It agrees with the nominal masses in BS 4449 and BS 8666 to about 0.1%: 10 mm 0.616, 12 mm 0.888, 16 mm 1.579, 20 mm 2.466, 25 mm 3.854, 32 mm 6.313 kg/m. Common UK sizes are 8, 10, 12, 16, 20, 25, 32 and 40 mm, delivered in 6 m and 12 m stock lengths or cut and bent to a schedule. Use the scheduled cutting length, not the drawn length.
Common mistake
Weighing a job from the drawn bar lengths, which leaves out laps, hooks and bends and under-orders the steel.
Limits
Nominal mass. BS 4449 allows a small rolling tolerance on actual mass per metre (larger for 8 mm and below). Stainless and galvanised bars have slightly different masses; use the supplier’s figure.
Sources
- BS 4449:2005+A3:2016 Steel for the reinforcement of concrete. Weldable reinforcing steel. Bar, coil and decoiled product
- BS 8666:2020 Scheduling, dimensioning, cutting and bending of steel reinforcement for concrete. Specification (Table 2 minimum radii and end projections; Table 5 standard shapes and length formulae)
- Celsa Steel UK, Reinforcing bars (BS 4449 B500C, CARES approved; 12 mm 0.888, 16 mm 1.579, 25 mm 3.854 kg/m; 6 m and 12 m stock lengths)
- CR Steel, Steel calculator sheet (bar mass per metre, metres per tonne, 12 m bars per tonne; BS 4483 mesh masses: A142 2.22, A193 3.02, A252 3.95, A393 6.16 kg/m²)
- UK CARES, Certification Authority for Reinforcing Steels (certification of reinforcing steel, fabricators and fixing)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.