Rebar Weight Calculator
Find the weight of reinforcing steel from bar diameter, number of bars and length. Add a row for each bar size in your schedule.
| Diameter | Bars | Length (m) | kg/m | Weight (kg) |
|---|
The rebar weight formula
Steel weighs about 7,850 kg/m³. Working that through the circular cross-section gives the standard site shortcut:
Weight per metre (kg/m) = d² ÷ 162, where d is the bar diameter in millimetres.
Total weight = weight per metre × length per bar × number of bars
In imperial terms, weight per foot in pounds is roughly d² ÷ 241 with d in millimetres. The calculator adds your laps and wastage percentage to the total length before working out the weight.
Worked example
You need 40 bars of 12 mm, each 6 m long, with 5% for laps and cuts.
- Weight per metre: 12² ÷ 162 = 0.889 kg/m
- Plain length: 40 × 6 = 240 m
- With 5% extra: 240 × 1.05 = 252 m
- Total weight: 252 × 0.889 = 224 kg
- Stock bars: 252 ÷ 12 = 21 bars of 12 m
Weight of common bar sizes
| Diameter (mm) | kg per metre | kg per 12 m bar | lb per foot |
|---|---|---|---|
| 6 | 0.222 | 2.67 | 0.149 |
| 8 | 0.395 | 4.74 | 0.265 |
| 10 | 0.617 | 7.40 | 0.415 |
| 12 | 0.889 | 10.67 | 0.598 |
| 16 | 1.580 | 18.96 | 1.062 |
| 20 | 2.469 | 29.63 | 1.660 |
| 25 | 3.858 | 46.30 | 2.593 |
| 32 | 6.321 | 75.85 | 4.249 |
Frequently asked questions
How much should I add for laps?
Lap length is usually 40 to 50 times the bar diameter, depending on the grade and code. For a rough estimate, 5 to 10% extra covers laps, hooks and cutting waste. Use your bar bending schedule for the exact figure.
Why is the formula d² ÷ 162?
The cross-section area is π d² ÷ 4, and multiplying by steel density (7,850 kg/m³) and converting millimetres to metres gives about d² ÷ 162.2.
Does bar grade change the weight?
No. Fe415, Fe500, Fe550 and similar grades differ in strength, not density, so the weight per metre is the same for a given diameter.
Do TMT bars weigh exactly the same as the table shows?
Standards allow a small tolerance on mass, commonly around plus or minus 3 to 7% depending on size. Check the mill certificate for delivered material.
How many bars come in a tonne?
Divide 1,000 by the weight of one bar. For 12 mm in 12 m lengths, one bar weighs about 10.67 kg, so a tonne is roughly 94 bars.
