Steel vs Aluminum: How Much Heavier Is Steel?
Steel is much heavier than aluminum for the same size, but the real comparison depends on what you are building. This guide gives the numbers and shows how to work out the weight of your own parts.
The density difference
Carbon steel has a density of about 7,850 kg/m³, while aluminum is about 2,700 kg/m³. Dividing the two gives 2.9, so a steel part is roughly 2.9 times heavier than an aluminum part of identical dimensions. Real alloys vary by a percent or two, so use your supplier’s figure when it matters.
Example: a round bar
A round bar with a diameter of 20 mm has a cross-section of about 314 mm². A metre of steel bar weighs 0.000314 × 7,850 ≈ 2.47 kg, and a metre of aluminum bar weighs 0.000314 × 2,700 ≈ 0.85 kg.
Plate weight per square metre
For a flat plate, weight per square metre is just thickness times density.
| Thickness | Steel | Aluminum |
|---|---|---|
| 1 mm | 7.85 kg/m² | 2.70 kg/m² |
| 2 mm | 15.70 kg/m² | 5.40 kg/m² |
| 3 mm | 23.55 kg/m² | 8.10 kg/m² |
| 5 mm | 39.25 kg/m² | 13.50 kg/m² |
| 10 mm | 78.50 kg/m² | 27.00 kg/m² |
Same stiffness is a different comparison
Aluminum is also less stiff than steel: its modulus of elasticity is about 69 GPa against roughly 200 GPa for steel. A plate loaded in bending gets stiffer with the cube of its thickness, so to match the stiffness of a steel plate an aluminum plate must be about 1.4 times thicker. Even then it ends up weighing about 49% as much as the steel plate, which is why aluminum is popular where weight matters, such as vehicles and ladders.
Strength is another story. Many aluminum alloys are weaker than structural steel, and the comparison depends on the alloy and the load. For structural work, rely on an engineer and the supplier’s data rather than on weight alone.
How to calculate the weight of your own part
- Find the cross-section area of the profile (plate, bar, tube or angle).
- Multiply by the length to get the volume.
- Multiply the volume by the density of the metal.
The Metal Weight Calculator does all of this for steel, stainless steel, aluminum, copper, brass and more, in kilograms and pounds, for bars, plates, tubes and angles.
Frequently asked questions
How much heavier is steel than aluminum? About 2.9 times heavier for the same volume, based on densities of 7,850 and 2,700 kg per cubic metre.
How much does a steel plate weigh per square metre? About 7.85 kg per square metre for each millimetre of thickness. A 10 mm plate is about 78.5 kg per square metre.
Is aluminum always the better choice for weight? Not always. It is lighter, but it is also less stiff and often weaker than steel, so the part may need to be thicker. Compare designs at equal stiffness or strength.
Which density should I use for stainless steel? About 8,000 kg per cubic metre is a common figure, a little higher than carbon steel.