How steel weight is calculated
Steel weight is the bar's cross-sectional area multiplied by its length and by the density of steel, 7,850 kg/m³. For a round bar or rebar that simplifies to weight (kg/m) = D² ÷ 162, with D in millimetres. Multiply the kg/m figure by the total length in metres to get the total weight.
This calculator covers six shapes: round bar, reinforcement bar (rebar), square bar, flat bar, angle, and round pipe or tube. Enter the dimensions in millimetres and the total length in metres. Only the fields for the shape you pick are used, so you can leave the others blank.
Formulas for each shape
Every formula below is steel's density (7,850 kg/m³, or 0.00785 kg per mm² per metre) applied to the shape's cross-section:
| Shape | Inputs (mm) | Weight per metre (kg/m) |
|---|---|---|
| Round bar / rebar | Diameter D | D² ÷ 162 |
| Square bar | Side S | 0.00785 × S² |
| Flat bar | Width W, thickness T | 0.00785 × W × T |
| Angle | Legs A and B, thickness T | 0.00785 × T × (A + B − T) |
| Pipe / tube | Outer diameter OD, wall T | 0.02466 × T × (OD − T) |
The angle formula treats the section as two rectangles that overlap in a T × T corner, which is why T is subtracted once. Rolled angles have rounded roots and toes, so a manufacturer's section table can differ slightly. The pipe constant 0.02466 is π × 0.00785.
The calculator checks that an angle's thickness is smaller than both legs and that a pipe's wall is less than half its outer diameter. It shows unit weight to 3 decimals, total weight in kg to 3 decimals, and tonnes to 4.
Worked example: rebar
You need 12 m of 12 mm rebar.
- Square the diameter: 12 × 12 = 144.
- Divide by 162: 144 ÷ 162 = 0.889 kg/m.
- Multiply by length: 0.889 × 12 = 10.667 kg, or 0.0107 t.
A standard 12 m length of 16 mm bar works out to 1.580 kg/m and 18.963 kg.
Worked example: flat bar and angle
- A 50 × 6 mm flat bar: 0.00785 × 50 × 6 = 2.355 kg/m. Six metres weigh 14.130 kg.
- A 50 × 50 × 6 mm angle: 0.00785 × 6 × (50 + 50 − 6) = 4.427 kg/m. Six metres weigh 26.564 kg.
- A 48.3 mm OD pipe with a 3.2 mm wall: 0.02466 × 3.2 × 45.1 = 3.559 kg/m.
Rebar weight table
The left column is what this calculator returns (D² ÷ 162). The right column is the nominal mass per metre from Table 1 of IS 1786:2008, the Indian standard for high-strength deformed reinforcing bars, which defines nominal mass using a density of 0.00785 kg/mm² per metre.
| Diameter (mm) | D² ÷ 162 (kg/m) | IS 1786 nominal mass (kg/m) |
|---|---|---|
| 6 | 0.222 | 0.222 |
| 8 | 0.395 | 0.395 |
| 10 | 0.617 | 0.617 |
| 12 | 0.889 | 0.888 |
| 16 | 1.580 | 1.58 |
| 20 | 2.469 | 2.47 |
| 25 | 3.858 | 3.85 |
| 32 | 6.321 | 6.31 |
The rule of thumb runs about 0.16% high because the exact constant is 162.2. On a full tonne of steel that's under 2 kg.
Estimating steel for a whole job
- List each bar size from the bar bending schedule or drawings, with its total cut length including laps and hooks.
- Run each size through the calculator, or multiply total length by the kg/m figure in the table.
- Add the sizes together and convert to tonnes for ordering.
- Add an allowance for offcuts. The calculator doesn't add wastage itself.
If you're working from a slab or beam, the RCC slab calculator and beam calculator give the concrete volume to pair with the steel figure. The weight converter turns kilograms into pounds or short tons, and the construction materials converter handles other material conversions.
Limits
Results assume carbon or mild steel at 7,850 kg/m³. Stainless steel and other alloys have different densities, so this will be a few percent off for them. Reinforcement sizes, spacing and laps for any structure must be specified by a qualified structural engineer under your local building code. This calculator estimates weight; it doesn't check design.
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