How this calculator works
A round bar is a cylinder, so its weight is volume multiplied by density. The calculator converts the diameter from millimetres to metres, finds the cross-sectional area, multiplies by length to get volume and by density to get mass, then scales by the number of bars.
Round bar weight formula
Weight (kg) = π ÷ 4 × d² × L × ρ, with d in metres, L in metres and ρ in kg/m³.
For mild steel (ρ = 7850 kg/m³) this simplifies to the familiar weight per metre = d² ÷ 162 with d in millimetres.
Worked example
Ten mild steel bars, 20 mm diameter and 6 m long. Weight per metre = π ÷ 4 × 0.02² × 7850 = 2.466 kg/m. One bar weighs 2.466 × 6 = 14.797 kg, so ten bars weigh 147.97 kg.
Typical densities
Approximate values: mild steel 7850 kg/m³, stainless steel about 7900–8000 kg/m³, aluminium about 2700 kg/m³, brass about 8400–8700 kg/m³ and copper about 8960 kg/m³. Use your supplier’s data sheet for exact grades.
How to use this calculator
- Enter the bar diameter in millimetres.
- Enter the length per bar and the number of bars.
- Keep density at 7850 for mild steel or type the density of your material.
- Select Calculate to see weight per metre, per bar and in total.
Frequently asked questions
How do I calculate the weight of a round bar?
Multiply π ÷ 4 by the diameter squared, the length and the material density, using consistent units. For steel in millimetres, diameter squared divided by 162 gives kilograms per metre.
What density should I use for steel?
Mild steel is normally taken as 7850 kg/m³. Stainless grades are slightly higher, so enter the value from the material certificate when precision matters.
Is the d²/162 rule exact?
It is an approximation for steel with a density of about 7850 kg/m³. The full formula in this calculator gives the same result to three significant figures for steel.
Does it include mill tolerance?
No. Rolled bars can weigh a little more or less than nominal. Allow for tolerance and cutting waste in purchase quantities.
Nominal calculated weight only. Confirm weights against the supplier’s bar schedule, tolerances and material certificates before ordering or design use.
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