Steel Weight Formula
Steel weight is density times volume. For common carbon and low-alloy steels, use ρ = 7.85 g/cm³ (7,850 kg/m³ or 0.284 lb/in³) unless the mill certificate gives a better value.
Open the metal weight calculatorSteel weight formula
The general steel weight formula is W = ρ · A · L where
ρ is density, A is cross-section area and L is length.
With density in g/cm³, area in mm² and length in mm:
weight (kg) = ρ · A · L / 1,000,000.
For mild steel, A36, 1018, 1045, 4140 and most low-alloy steels, the practical stock density is 7.85 g/cm³. Stainless is usually a little heavier at about 8.00 g/cm³, while cast iron is lighter around 7.1-7.3 g/cm³.
Common steel stock shortcuts
- Round bar:
kg/m = 7.85 · π · d² / 4000, with d in mm. - Plate:
kg = 7.85 · width · thickness · length / 1,000,000, all dimensions in mm. - Round tube or pipe:
kg/m = 7.85 · π/4 · (OD² - ID²) / 1000, with diameters in mm.
Worked example
A 25 mm diameter mild-steel round bar has
A = π/4 × 25² = 490.9 mm². Its weight per metre is
7.85 × 490.9 / 1000 = 3.85 kg/m. A 1 m length weighs
3.85 kg, and a 6 m stock length weighs about 23.1 kg.
When the shortcut is not enough
The 7.85 g/cm³ value is right for estimates and purchasing checks, but exact shipped weight depends on alloy chemistry, stock tolerances, coatings, scale and any weld bead inside tube. For a quote, freight estimate or critical assembly mass, run the actual dimensions in the calculator and verify the density against the material certificate.
Related material tools
- Metal weight calculator for bar, tube, plate, angle and material changes.
- Material density chart for steel, aluminum, stainless, brass, bronze, titanium and plastics.
- Steel pipe schedule chart for nominal pipe sizes, wall thickness and IDs.
- Aluminum weight formula for a focused formula and worked example.
- Stainless steel weight formula for a focused formula and worked example.
- Round bar weight formula for a focused formula and worked example.
- Plate weight formula for a focused formula and worked example.
- Pipe weight formula for a focused formula and worked example.
- Square tube weight formula for a focused formula and worked example.
- Rectangular tube weight formula for a focused formula and worked example.
Last reviewed: June 1, 2026.