Kumar IronUpdated
In this guide
The formula: weight per metre = D² ÷ 162
D is the bar diameter in millimetres. The answer is kilograms per metre. For a 12 mm bar, 12 × 12 = 144, and 144 ÷ 162 = 0.889 kg per metre.
It comes from the density of steel, about 7850 kg per cubic metre, multiplied by the cross-section area of the bar. The grade does not change it: Fe500, Fe500D and Fe550D bars of the same diameter weigh the same.
Bars per tonne, by diameter
| Diameter | kg per metre | kg per 12 m bar | Bars per tonne (approx.) |
|---|---|---|---|
| 8 mm | 0.395 | 4.74 | 211 |
| 10 mm | 0.617 | 7.40 | 135 |
| 12 mm | 0.889 | 10.67 | 94 |
| 16 mm | 1.580 | 18.96 | 53 |
| 20 mm | 2.469 | 29.63 | 34 |
| 25 mm | 3.858 | 46.30 | 22 |
| 32 mm | 6.321 | 75.85 | 13 |
Some mills roll bars slightly longer than 12 m, such as 12.2 m, so the per bar weight and count per tonne shift a little. Ask the dealer the bar length for the brand you buy.
Rolling tolerance: why actual weight differs
IS 1786 allows each bar to be a little lighter or heavier than the theoretical weight. Thinner bars get a wider allowance than thick ones. A bundle that is consistently at the bottom of the tolerance gives you less steel per kg paid. Our delivery check guide shows how to weigh a sample bar on site.
Five mistakes that cost money
- Using one average weight for all sizes. 8 mm and 16 mm differ fourfold per metre.
- Counting bars per tonne from a 12 m chart when the brand rolls a different length.
- Converting diameter in cm or inches instead of mm. The formula only works in mm.
- Ignoring laps and cutting waste, then running short on the casting day.
- Comparing a per bar rate from one dealer with a per kg rate from another without converting.
Frequently asked questions
- How many 12 mm bars are in one tonne?
- About 94 bars of 12 m length, since each weighs about 10.67 kg.
- Does a higher grade bar weigh more?
- No. Weight depends only on diameter and length. Grade changes strength, not weight.
- Should I be billed on actual or theoretical weight?
- Ask before you order. Actual weighed weight is fairer if bars run light. Either way, know which one the bill uses.