The weight of a steel bar in kg per metre is D² ÷ 162, where D is the bar diameter in mm. For example, a 12 mm bar weighs 144 ÷ 162 = 0.889 kg/m, so one 12 m length weighs about 10.67 kg.
Site engineers and overseers in Nepal use this formula every day to check steel deliveries, prepare bar bending schedules and estimate costs. Here is where it comes from and a ready table.
Where the D²/162 formula comes from
Weight of 1 m of bar = density × cross-section area × length.
- Density of steel = 7850 kg/m³
- Area = π/4 × D², and with D in mm this is π/4 × D² ÷ 1,000,000 m²
- Length = 1 m
So weight = 7850 × 0.7854 × D² ÷ 1,000,000 = 0.0061654 × D² kg/m. And 1 ÷ 0.0061654 = 162.2, which is rounded to 162. That gives the easy form D²/162.
Weight of steel bars per metre: table
| Diameter (mm) | kg per metre (D²/162) | kg per 12 m bar | kg per foot |
|---|---|---|---|
| 8 | 0.395 | 4.74 | 0.120 |
| 10 | 0.617 | 7.41 | 0.188 |
| 12 | 0.889 | 10.67 | 0.271 |
| 16 | 1.580 | 18.96 | 0.482 |
| 20 | 2.469 | 29.63 | 0.753 |
| 25 | 3.858 | 46.30 | 1.176 |
| 32 | 6.321 | 75.85 | 1.927 |
kg per foot = kg per metre × 0.3048. The IS 1786 nominal mass table uses the exact 7850 kg/m³ value, so its figures for the larger bars are a little lower (for example 3.85 kg/m for 25 mm and 6.31 kg/m for 32 mm). The difference is about 0.1 to 0.2%, which does not matter for site estimates.
Worked example
A column cage uses 10 bars of 16 mm, each 12 m long. Weight = 10 × 12 × 256 ÷ 162 = 189.6 kg. For a quick check of a whole tonne: 1000 ÷ 10.67 = about 94 lengths of 12 mm bar make one tonne.
The steel weight calculator works this out for any diameter, length and number of bars. To see how steel fits into a full house estimate, use the house construction cost estimator.
Frequently asked questions
What is the weight of an 8 mm bar per foot?
About 0.120 kg per foot, from 0.395 × 0.3048.
Why does a delivered bar weigh slightly less than the table?
Rolled bars have a small tolerance on mass per metre under IS 1786, and thin bars are allowed a wider tolerance than thick ones. Weigh a few sample lengths when you receive steel and compare with the table.
Does the formula work for TMT bars?
Yes. TMT and other deformed bars are specified by nominal diameter, and the nominal mass is based on the same 7850 kg/m³ density.
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