The formula
This comes from steel's density (7,850 kg/m³) applied to a bar's circular cross-sectional area, simplified into a single divisor. It's the same formula published in steel mill weight tables worldwide — a 12mm bar works out to 0.888 kg/m, matching standard rebar weight charts.
Common bar sizes
Metric rebar is typically supplied in 8, 10, 12, 16, 20, 25, and 32mm diameters. US rebar uses numbered sizes instead — #3 (⅜″), #4 (½″), #5 (⅝″), #6 (¾″), and #8 (1″) are the most common on residential and light commercial work.
Frequently asked questions
Why divide by 162 specifically?
It comes from combining steel's density (7,850 kg/m³) with the geometry of a circular cross-section and unit conversion to kg per metre run — the constants simplify to 162 when diameter is entered in millimetres.
Does this account for bar overlap/laps at splices?
No — this gives raw bar weight for the length entered. If you're pricing a full reinforcement schedule, add extra length for lap splices per your structural drawing (commonly 40-50× bar diameter per lap).
Is this accurate for both mild steel and TMT/deformed bars?
Yes — the formula is based on cross-sectional area and steel density, which is essentially the same for mild steel and deformed (ribbed) bars of the same nominal diameter.