Material properties comparison
Density, strength, and stiffness side by side for the most common engineering materials, from steels and aluminums to titanium and plastics. Use it to weigh strength against weight and stiffness when choosing a material.
Common engineering materials
| Material | Density (lb/in³) | Yield (ksi) | Tensile (ksi) | Modulus (Mpsi) |
|---|---|---|---|---|
| Carbon steel (A36) | 0.284 | 36 | 58 | 29 |
| Alloy steel (4140) | 0.284 | 95 | 115 | 29 |
| Stainless steel (304) | 0.289 | 31 | 75 | 28 |
| Aluminum (6061-T6) | 0.098 | 40 | 45 | 10 |
| Aluminum (7075-T6) | 0.102 | 73 | 83 | 10.4 |
| Titanium (Grade 5) | 0.160 | 128 | 138 | 16.5 |
| Magnesium (AZ31) | 0.064 | 22 | 37 | 6.5 |
| Brass | 0.307 | 18 | 50 | 15 |
| Copper | 0.323 | 10 | 32 | 17 |
| Cast iron (gray) | 0.260 | — | 30 | 14 |
| Polycarbonate | 0.043 | 9 | 9 | 0.34 |
| Nylon 6/6 | 0.041 | 12 | 12 | 0.4 |
| ABS | 0.038 | 6 | 6 | 0.30 |
Yield and tensile are typical values; modulus (the Young modulus) is the stiffness in millions of psi. Notice that all steels share nearly the same modulus near 29 Mpsi regardless of strength, while aluminum is about one third as stiff but also one third the weight. Cast iron is brittle and rated by tensile rather than yield.
Want one property in depth?
See the Material Density, Yield Strength, and Hardness charts for full tables.
Strength vs stiffness vs weight
These three properties are independent. Strength (yield and tensile) is the load a material carries before yielding or breaking. Stiffness (modulus) is how much it deflects under load and barely changes with alloy. Weight comes from density. A part can be strong but flexible, or stiff but heavy, so the right material depends on which property drives the design.
Strength-to-weight matters
Dividing strength by density gives specific strength, where aluminum and titanium shine. Titanium is as strong as steel at well under half the weight, and aluminum carries useful load at one third the weight, which is why aerospace leans on them despite higher cost. For stiffness-driven parts, steel often wins because aluminum deflects about three times as much.
FAQ
Which is stronger, steel or aluminum?
Steel is generally stronger and much stiffer. But high-strength aluminum like 7075 rivals mild steel at one third the weight, so aluminum can win on strength-to-weight.
Why do all steels have the same stiffness?
The Young modulus depends on atomic bonding, which alloying barely changes. So mild and alloy steels share a modulus near 29 Mpsi even though their strengths differ widely.
What material has the best strength-to-weight ratio?
Among common metals, titanium and high-strength aluminum lead. Titanium Grade 5 matches steel strength at under half the weight.