What this calculator does
Metal weight is volume times density, and the density range across common metals is wide. The same one metre bar of 100 by 5 mm section weighs 1.350 kg in aluminium and 5.670 kg in lead, a factor of more than four.
That spread is why substituting materials changes far more than the price. Aluminium at 2,700 kg/m³ is roughly a third the weight of steel at 7,850 for the same section, which is the whole reason it is used in aircraft and ladders despite costing more per kilogram.
The formula
The volume is length times width times thickness for a rectangular section, or pi times the radius squared times length for a round one. Multiplying by the density gives the weight. The densities are nominal values for each material; specific alloys vary by a percent or two, which rarely matters for an estimate.
| Term | Meaning |
|---|---|
| Density | Mass per unit volume. Mild steel is 7,850 kg/m³, aluminium 2,700. |
| Section | The cross-sectional shape and dimensions of the bar or plate. |
| Nominal density | A representative figure for the material. Specific alloys differ slightly. |
| Specific gravity | Density relative to water. Steel is about 7.85, aluminium 2.7. |
The inputs explained
| Field | What to enter |
|---|---|
| Shape | Rectangular plate or bar, or round rod. |
| Length (mm) | Length in millimetres. |
| Width (rectangular only) (mm) | Width, for a rectangular section only. |
| Diameter (round only) (mm) | Diameter, for a round section only. |
| Thickness (rectangular only) (mm) | Thickness, for a rectangular section only. |
| Material | Material, which sets the density. |
When to use it
Estimating a fabrication
Steel is priced by weight, so the weight is the cost.
Checking a lifting plan
Knowing what a section weighs determines whether it can be handled manually.
Comparing materials
Substituting aluminium for steel cuts the weight to roughly a third for the same section.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does the material matter?
The same section in a range of materials.
| Material | Weight | In pounds | Volume |
|---|---|---|---|
| Aluminium | 1.350 kg | 2.98 lb | 500.00 cm³ |
| Mild steel | 3.925 kg | 8.65 lb | 500.00 cm³ |
| Copper | 4.480 kg | 9.88 lb | 500.00 cm³ |
| Lead | 5.670 kg | 12.50 lb | 500.00 cm³ |
Questions
Why is aluminium used where steel would be cheaper?
Because it weighs about a third as much for the same section. Where the structure has to move, fly or be carried, the weight saving is worth the higher price per kilogram. For a static structure where weight does not matter, steel is usually the better value.
Do specific alloys differ from these densities?
Slightly. Mild steel grades cluster very close to 7,850 kg/m³, and aluminium alloys range from about 2,650 to 2,800. Stainless varies more between grades. For estimating, the nominal figures are fine; for precision work, use the alloy specification.
Is copper really heavier than steel?
Yes, at 8,960 against 7,850 kg/m³, about 14% heavier. It surprises most people because steel feels like the archetypal heavy metal. Lead at 11,340 is heavier again, though still well short of denser metals such as tungsten or gold.
How do I handle a hollow section?
Calculate the outer volume and subtract the inner. For a tube, run the round calculation at the outside diameter, then again at the inside diameter, and take the difference. The same approach works for any hollow shape.
For timber weights instead, see the lumber weight calculator. For punching and bending, see the punch force calculator.