Steel weights
Round and square bar weight per metre
- where
- round bar mass per metre (kg/m)
- diameter or side (mm)
- steel density (kg/m³)
- square bar mass per metre (kg/m)
- round bar total mass (kg)
- total length (m)
- square bar total mass (kg)
Explain this equation
Gives the weight per metre and total weight of round and square bar of the same size.
A round bar's cross-section is a circle, πd²/4; a square bar's is d². Area in mm² times a metre of length is 10⁻⁶ cubic metres per mm², which is why dividing by a million and multiplying by density gives kilograms per metre. Times the length gives the total.
Mass per length is cross-section area times density.
Sense check: 20 mm round is about 2.47 kg/m and 20 mm square about 3.14 kg/m. A round bar is always π/4, about 79%, of the square bar's weight.
Watch out: doubling the diameter quadruples the weight.
Mass per metre and total mass of solid round bar (diameter d) or square bar (side d).
Enter your values to see the result.
Good to know
Density 7850 kg/m³ as used for nominal steel masses. Handy check: round bar mass in kg/m is about d² / 162 (d in mm); square bar is d² / 127.4. Hexagon bar (across flats d) is 0.866 × the square-bar figure.
Common mistake
Using the diameter as the radius, which gives four times the weight, or confusing the square bar side with its across-corners dimension.
Limits
Nominal mass from nominal size; bright and hot-rolled bars have different size tolerances.
Sources
- BS EN 10365:2017 Hot rolled steel channels, I and H sections – Dimensions and masses (density 7850 kg/m³)
- BS EN 10219-2:2019 Cold formed welded steel structural hollow sections – Part 2: Tolerances, dimensions and sectional properties (mass from density 7.85 kg/dm³; corner radius rules and area formula)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the welding procedure specification (WPS), BS EN ISO 15614/9606, BS EN 1090, BS EN 1993 and manufacturers’ data. Structural welds need qualified welders and engineered designs.