Material densities and part mass calculator
Published September 28, 2026 — densities of steels, aluminium alloys, copper alloys, titanium and engineering plastics, a mass calculator for plates, bars, tubes and hex stock, and the SOLIDWORKS settings that keep BOM mass correct.
Part mass calculator
Pick the material and shape, enter the dimensions in millimetres: you get the volume and mass. Handy for a quote, a BOM, or to check the mass computed by CAD.
Rule of thumb: a 1 m × 1 m × 1 mm steel plate weighs 7.85 kg. In aluminium, 2.7 kg — almost three times less, for the same volume.
1. Densities of metals
Usual values at 20 °C. For a given alloy, the supplier's material data sheet or the grade standard prevails; differences between grades in the same family are typically 1 to 3%.
2. Densities of plastics
Plastics vary more: fillers (glass fibre, mineral), crystallinity and additives shift the value. A 30% glass-filled PA6 is clearly heavier than unfilled PA6: use the data sheet of the exact grade.
Other materials:
3. The formulas used
- Mass = density × volume. With dimensions in mm: m (kg) = ρ (kg/m³) × V (mm³) × 10−9.
- Plate: V = L × w × t.
- Round bar: V = π × D² / 4 × L.
- Tube: V = π × (D² − d²) / 4 × L, with d = D − 2 × wall.
- Hex bar (across flats s): V = (√3 / 2) × s² × L.
Example: a 1 m long Ø 50 steel bar weighs π × 50² / 4 × 1,000 × 7,850 × 10−9 ≈ 15.4 kg.
4. In SOLIDWORKS: a correct mass all the way to the BOM
SOLIDWORKS computes mass from the material applied to the part (right-click Material → Edit Material) and shows it in Tools → Evaluate → Mass Properties. Three things make the difference between a reliable and a wrong mass:
- No material, no mass: a part without material takes the default density (1,000 kg/m³, that of water). A BOM full of “1,000” parts gives assembly masses off by a factor of 8 for steel.
- Mass as a linked property: the Mass custom property must be linked to the computed value (
"SW-Mass@…"), never typed by hand, or it stops following changes. - Downloaded purchased parts often have an empty or wrong material: a check at check-in to PDM keeps them from polluting the BOM.
These are typically the rules of good SOLIDWORKS property codification, so that mass arrives correct in the BOM and the ERP.
5. FAQ
What is the density of steel?
7,850 kg/m³ (7.85 g/cm³) for carbon and low-alloy steels. Austenitic stainless steels are slightly heavier: about 7,900 kg/m³ for 304 and 8,000 kg/m³ for 316L.
What is the density of aluminium?
2,700 kg/m³ (2.7 g/cm³) for aluminium and the common 6060, 6061 and 6082 alloys. Copper or zinc alloys are slightly denser: about 2,790 kg/m³ for 2017A and 2,810 kg/m³ for 7075.
How much does a 1 mm steel sheet weigh?
7.85 kg per square metre. The rule generalises: a steel sheet weighs 7.85 kg/m² per millimetre of thickness, i.e. 23.55 kg/m² at 3 mm.
How do I calculate the mass of a steel round bar?
Mass (kg/m) = π × D² / 4 × 7,850 × 10⁻⁶, with D in mm. Quick formula: D² × 0.00617 kg per metre. A Ø 50 therefore weighs about 15.4 kg/m.
Why is the SOLIDWORKS mass wrong?
Most often because some parts have no material applied: SOLIDWORKS then uses the default density of 1,000 kg/m³. Check each part's material and that the Mass property is linked to the computed value.