Reinforcement is priced in kg in the budget but bought in 12 m bars. So there are two steps: work out the total length of each diameter from the reinforcement drawings, then convert it to kg for the budget and to bars for purchasing.
The weight-per-metre formula
Weight (kg per metre) = 0.00617 × d², with d the diameter in mm. For a 13 mm bar: 0.00617 × 13 × 13 = 1.04 kg per metre.
| Diameter | Weight per metre | Weight per 12 m bar |
|---|---|---|
| 8 mm | 0.395 kg | 4.74 kg |
| 10 mm | 0.617 kg | 7.40 kg |
| 12 mm | 0.888 kg | 10.66 kg |
| 13 mm | 1.04 kg | 12.48 kg |
| 16 mm | 1.58 kg | 18.95 kg |
Example: a 15/20 ground beam, 34 m long
The ground beam from the example house in the BOQ article, with 4 D10 main bars and 8 mm stirrups at 150 mm, 25 mm concrete cover.
| Part | Calculation | Length | Weight |
|---|---|---|---|
| Main bars 4 D10 | 4 × 34 m = 136 m, plus 10% for laps and hooks | 149.6 m | 149.6 × 0.617 = 92.3 kg |
| Stirrups 8 mm at 150 | Inside size 100 × 150 mm: perimeter 0.50 m + hooks 0.12 m = 0.62 m each; count 34 ÷ 0.15 + 1 = 228 | 141.4 m | 141.4 × 0.395 = 55.8 kg |
| Total | 148.1 kg |
Number of 12 m bars: D10 149.6 ÷ 12 = 12.5, so 13 bars; 8 mm 141.4 ÷ 12 = 11.8, so 12 bars. Add about 3% to 5% for offcuts if they cannot be used elsewhere.
The bar bending schedule
The bending schedule lists every bar shape: mark, diameter, shape, cut length, number and weight. The steel fixers cut from 12 m bars with as little waste as possible, and the supervisor can check installed bars against the drawings.
| Mark | Diameter | Shape | Cut length | Number | Weight |
|---|---|---|---|---|---|
| S1 | D10 | Straight with end hooks | per span length | 4 per span | worked out |
| S2 | 8 mm | Closed stirrup 100 × 150 | 0.62 m | 228 | 55.8 kg |
Common mistakes
- Forgetting lap lengths. They are set by the drawings and the concrete code, often about 40 times the diameter.
- Measuring stirrups on the outside of the concrete instead of inside the cover.
- Delivered bars lighter than nominal weight (undersized bars). Weigh a sample when the steel arrives.
- Steel worked out in kg but ordered in bars without allowing for offcuts.
The full guide is in How to build a construction cost report that catches overruns early. It has a free template (Excel or Google Sheets) and a checker that reads your own workbook.
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Common questions
What is the formula for rebar weight?
Weight per metre = 0.00617 × d², with d the diameter in mm. 10 mm = 0.617 kg per metre, 13 mm = 1.04 kg per metre.
How much does one 13 mm bar weigh?
A 12 m bar is about 12.48 kg, at the nominal 1.04 kg per metre.
How long are rebar laps?
As the drawings and concrete code say; in practice often about 40 times the diameter.
What is a bar bending schedule?
The cutting and bending list: every bar shape with its diameter, cut length, number and weight.
References
- SNI 07-2052-2002 reinforcing steel (Indonesian): nominal diameters and weights; check for a newer edition