Key takeaways
- Weight per metre (kg/m) = d² ÷ 162, with d in millimetres.
- The 162 bundles together π/4, steel density 7,850 kg/m³, and the mm-to-m conversion.
- For weight per foot use d² ÷ 533 instead.
- Total weight = kg/m × bar length × number of bars.
The quick answer
The weight of a round steel bar, in kilograms per metre, is its diameter squared divided by 162: kg/m = d² ÷ 162, where d is the nominal diameter in millimetres. A 12 mm bar is 12² ÷ 162 = 144 ÷ 162 = 0.888 kg/m. Multiply by the bar length and the number of bars to get the total order weight. For imperial sites the per-foot version is d² ÷ 533.
Where 162 comes from
The weight of a bar is just its cross-sectional area times the density of steel. Start from the area of a circle, A = (π ÷ 4) × d², with d in mm. Multiply by steel's density (7,850 kg/m³) and divide by 1,000,000 to convert mm² to m². Collapsing the constants:
So 162 is not arbitrary — it is 1 ÷ 0.0061654, rounded. The same logic gives the per-foot constant: 162.28 × 3.281 ft/m ≈ 532.6, rounded to 533. The steel weight calculator applies these constants for any diameter, length and bar count.
Per-metre weight reference table
These are the standard rebar diameters and their unit weights from d²/162. Steel is normally sold in tonnes, so these per-metre figures are what convert a cutting list into a purchase order.
| Bar dia (mm) | Weight (kg/m) | Weight (kg/ft) | Per 12 m bar |
|---|---|---|---|
| 8 | 0.395 | 0.120 | 4.74 kg |
| 10 | 0.617 | 0.188 | 7.40 kg |
| 12 | 0.888 | 0.270 | 10.66 kg |
| 16 | 1.580 | 0.481 | 18.96 kg |
| 20 | 2.469 | 0.751 | 29.63 kg |
| 25 | 3.858 | 1.174 | 46.30 kg |
| 32 | 6.321 | 1.924 | 75.85 kg |
A worked example: a bundle of 16 mm bars
You need 25 bars of 16 mm rebar, each 12 m long, for a beam. Step by step: weight per metre = 16² ÷ 162 = 256 ÷ 162 = 1.580 kg/m. Per bar that is 1.580 × 12 = 18.96 kg. For all 25 bars: 18.96 × 25 = 474 kg, or about 0.474 tonne. At a rate of, say, Rs 280,000 per tonne the steel for this bundle is roughly Rs 132,700 at current local pricing.
This is exactly how a bar-bending schedule is totalled: compute kg/m per diameter, multiply by cut length and quantity, then sum by diameter before ordering by weight.
From bars to a whole slab
For a reinforced slab you usually do not list every bar — you estimate steel as a rate per cubic metre of concrete (around 80 kg/m³ for a typical slab) and refine later with a bar schedule. The RCC slab calculator uses that rate to give a quick steel estimate alongside the concrete quantities.
Frequently asked questions
What is the d²/162 formula for steel weight?
Weight per metre (kg/m) = d² ÷ 162, with d the bar diameter in mm. A 12 mm bar is 144 ÷ 162 = 0.888 kg/m.
Where does the number 162 come from?
It is (π/4) × density (7,850 kg/m³) ÷ 1,000,000 inverted — the constants give d² ÷ 162.28, rounded to 162.
How do I get weight per foot instead of per metre?
Use d² ÷ 533, which folds the 3.281 ft/m conversion into the 162 constant.
Sources: the d²/162 (kg/m) and d²/533 (kg/ft) formulas derive from the circular cross-section area (π/4 · d²) and the standard steel density of 7,850 kg/m³, consistent with standard trade practice for HYSD/TMT reinforcement-bar unit weights. Per-metre values rounded to three decimals.
Last reviewed 2026-06-14