Rebar Weight & BBS Calculator
What is a Rebar Weight Calculator?
Reinforcement steel is bought and paid for by weight, but drawings specify it by diameter, length and number of bars. This calculator converts between them using the standard unit-weight formula, so you can estimate steel quantities, check supplier invoices and plan orders.
How to use it
- Choose the bar diameter.
- Enter the length of each bar and the number of bars.
- Read the weight per metre, per bar and in total, in kilograms and tonnes.
The d²/162 formula
Steel has a density of about 7850 kg/m³. The weight of a round bar per metre is the cross-sectional area times density: π × d² / 4 × 7850 / 10⁶ = d² / 162.2 kg/m, with d in millimetres. In practice d²/162 is used.
Unit weights
- 6 mm: 0.222 kg/m
- 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
Worked example
40 bars of 16 mm, each 12 m long: 1.58 × 12 = 18.96 kg per bar, so 40 bars weigh 758 kg, about 0.76 tonnes.
Practical tips
- Standard bar length is 12 m in many markets; count laps and cut lengths to minimise waste.
- Add about 3 to 5% for wastage and laps when ordering.
- Rolling tolerances mean actual weights vary slightly; codes such as IS 1786 allow a few percent deviation.
- For detailed quantities, prepare a bar bending schedule with cutting lengths for each bar shape.
Frequently Asked Questions
How do I calculate rebar weight per metre?
Square the diameter in millimetres and divide by 162. For a 12 mm bar, 144 divided by 162 is 0.889 kg per metre.
Where does the number 162 come from?
It comes from the cross-sectional area of a round bar multiplied by the density of steel, about 7850 kg per cubic metre.
How much does a 12 m bar of 16 mm weigh?
About 19 kg: 1.58 kg per metre multiplied by 12 metres.
Why does the actual weight differ from the calculated weight?
Manufacturing tolerances allow small deviations in bar diameter, so delivered weights vary by a few percent.