How steel weight is calculated
The 7850 kg/m³ density behind reinforcement weight tables, with a worked round-bar example.
Steel weight is volume multiplied by density. For carbon steel, including reinforcement bar, the conventional density is 7850 kilograms per cubic metre. Once the cross-section is known, weight per metre follows directly.
Round bar
A round bar of diameter d millimetres has an area of πd²/4 square millimetres. Dividing by one million converts that area into square metres per metre of length. Multiplying by 7850 gives kilograms per metre. A 12 mm bar is 0.888 kg/m. A 16 mm bar is 1.578 kg/m. The shop formula d²/162 is the same calculation, rounded.
A worked example
Ten 16 mm bars, each 12 metres long, weigh about 189.4 kg before laps, hooks or cutting waste. Those extras are not inside the section weight. Add them from the bar schedule, or start from the rebar estimator when you are laying bars out by spacing.
Plate is different only in shape: length, width and thickness, in metres, multiplied by 7850. Equal angle uses the approximate area (2 × leg − thickness) × thickness, which ignores the root radius. Treat the result as a planning figure and confirm it against the drawings before you order.