Aluminum is the material a designer reaches for when weight matters, and the number behind that decision is density: 2.70 g/cm³ for pure aluminium, against 7.85 g/cm³ for steel and 8.96 g/cm³ for copper. Roughly a third of steel, part for part - but only if the part is designed for it, because aluminum also has a third of the stiffness.
What is the density of aluminum?
Pure aluminum has a density of 2.70 g/cm³ (2,700 kg/m³, or 0.098 lb/in³) at room temperature. Commercial alloys sit between about 2.63 and 2.85 g/cm³ depending on what is alloyed in: 5052 at 2.68, 6061 at 2.70, 3003 at 2.73 and 7075 at 2.81. To get the weight of a part, multiply the volume in cm³ by the density - a 1,000 cm³ blank in 6061 weighs 2.70 kg, and the same blank in steel would weigh 7.85 kg. Density changes slightly with temperature and with temper, but not enough to matter for part weight, packing lists or freight calculations.
Density of the alloys we see on drawings
| Material | Density (g/cm³) | kg/m³ | Compared with steel |
|---|---|---|---|
| Aluminum 1050 (pure) | 2.70 | 2,700 | 34% |
| Aluminum 3003 | 2.73 | 2,730 | 35% |
| Aluminum 5052 | 2.68 | 2,680 | 34% |
| Aluminum 6061 | 2.70 | 2,700 | 34% |
| Aluminum 6082 | 2.70 | 2,700 | 34% |
| Aluminum 7075 | 2.81 | 2,810 | 36% |
| Steel (mild, DC01) | 7.85 | 7,850 | 100% |
| Stainless 304 | 8.00 | 8,000 | 102% |
| Copper C11000 | 8.96 | 8,960 | 114% |
| Brass (CuZn37) | 8.44 | 8,440 | 108% |
Turning density into part weight
Weight equals volume multiplied by density, and for a stamped or drawn part the volume comes from the blank, not from the finished geometry: sheet thickness multiplied by the developed area, less the scrap that is trimmed away. That is why material utilisation and weight are the same conversation. For a flat part it is quick arithmetic; for a drawn housing it is worth calculating from the blank, because the wall thins and the flange thickens and the finished part does not weigh exactly what the blank did. See thickness and gauge conversion when the drawing is still written in gauge.
What aluminum's density does and does not buy you
- Weight: yes - a third of the mass for the same volume, which is why it wins in transport, handheld devices and anything that has to be lifted repeatedly.
- Stiffness: no - Young's modulus is about a third of steel's, so a deflection-limited part often needs a thicker section or a rib, and the weight advantage narrows.
- Freight and packing - a lighter part is cheaper to ship, and the freight saving is real money on a programme that ships by air.
- Thermal behaviour - aluminum conducts heat better than steel and expands more, both of which matter on a housing that has to keep a sensor at temperature.
- Cost per kilogram - aluminum costs more per kilogram than steel, so the saving has to come from weight, corrosion resistance or process, not from material price.
Common conversions
| Unit | Aluminum | Steel |
|---|---|---|
| g/cm³ | 2.70 | 7.85 |
| kg/m³ | 2,700 | 7,850 |
| lb/in³ | 0.098 | 0.284 |
| lb/ft³ | 169 | 490 |
| kg per m² at 1 mm thick | 2.70 | 7.85 |
Key point
Use 2.70 g/cm³ for aluminium alloys in any first-pass weight calculation, and 2.68 for 5052 or 2.81 for 7075 when the drawing names the alloy. Calculate from the blank rather than the finished part for anything drawn, and remember that the third-of-steel weight comes with a third-of-steel stiffness.
Frequently asked questions
What is the density of aluminum in kg/m3?
2,700 kg/m³ for pure aluminum. Commercial alloys range from about 2,630 to 2,850 kg/m³.
Is aluminum lighter than steel?
Yes, by volume: 2.70 g/cm³ against 7.85 g/cm³ for mild steel, so an identical solid section is about a third of the weight. A part designed to a stiffness limit may end up heavier than the ideal ratio suggests, because aluminum is also less stiff.
What is the density of 6061 aluminum?
2.70 g/cm³, effectively the same as pure aluminum for weight calculations.
How do I calculate the weight of an aluminum part?
Multiply the volume in cm³ by 2.70 for pure or 6061 aluminium, or by the density of the specific alloy on the drawing. For sheet parts, start from the blank area multiplied by thickness.