Quick Answer
Pure aluminum has a density of 2.70 g/cm³ (2,700 kg/m³, 0.0975 lb/in³). Alloying moves it only slightly: common casting and wrought alloys span roughly 2.66–2.81 g/cm³. For quick estimates, 2.7 is accurate within about 2% for nearly every aluminum part you will ever buy — roughly one-third the density of steel (7.85) and iron (7.1–7.3).
Density Reference Table
| Material | Density (g/cm³) | Notes |
|---|---|---|
| Pure aluminum (1050/1100) | 2.70 | The baseline |
| A356 / 356 (Al-7Si-Mg) | 2.68 | Structural casting default |
| ADC12 / A380 (Al-Si-Cu) | 2.74–2.76 | Die casting workhorse |
| 6061 (Al-Mg-Si) | 2.70 | Wrought general purpose |
| 7075 (Al-Zn-Mg-Cu) | 2.81 | Highest-strength wrought, zinc-heavy |
| 5083 (Al-Mg) | 2.66 | Marine plate, lightest common alloy |
| For contrast: gray iron | 7.1–7.3 | ~2.6× aluminum |
| For contrast: steel | 7.85 | ~2.9× aluminum |
Calculating Casting Weight (With a Real Example)
Weight = volume × density. A pump housing with a CAD-reported volume of 850 cm³ in A356:
850 cm³ × 2.68 g/cm³ = 2,278 g ≈ 2.28 kg
Practical notes buyers should apply:
- Use the CAD solid volume of the final machined part for shipped weight; add machining stock and gating for pour-weight (foundry’s concern, but it drives quotes)
- Real castings run marginally lighter than theory when microporosity exists — typically under 1% difference in gravity/low-pressure work
- Steel-to-aluminum conversion at equal geometry cuts mass ~65% — but check stiffness: aluminum’s elastic modulus is one-third of steel’s, so sections often grow
Why Alloy Density Barely Moves
Silicon (2.33) nudges density down — hence A356 and 5083 sit below pure Al. Copper (8.96) and zinc (7.14) push it up — hence ADC12 and 7075 sit above. But at the few-percent alloying levels involved, the swing stays within ±4%, which is why 2.7 works as the universal estimate.
Where Weight Actually Decides the Alloy
- Rotating and reciprocating parts — every gram is inertia; A356-T6’s strength-to-weight earns its keep
- Shipping-cost-sensitive exports — casting weight prices freight; the density table feeds the landed-cost sheet
- Handheld products — ADC12’s slight extra density versus A356 is invisible; wall design dominates
For the strength side of the aluminum decision, see the A356 alloy guide and our cast vs wrought aluminum comparison. Aluminum structural parts at YCUMETAL run through gravity and low-pressure casting.
FAQ
Is cast aluminum less dense than wrought?
Chemistry decides density, not process. A356 casting (2.68) vs 6061 plate (2.70) differ by silicon content, not by being cast or rolled.
What is aluminum’s density in lb/in³?
0.0975 lb/in³ for pure aluminum; 0.096–0.102 across common alloys.
Does porosity change part weight noticeably?
Only in poor-quality high-pressure die castings. Gravity and low-pressure parts measure within ~1% of theoretical.