Thermal expansion coefficients
Coefficients of linear thermal expansion for common materials, per degree Celsius and per degree Fahrenheit. The value is how much a unit length grows for each degree of temperature rise, in parts per million.
Linear expansion coefficient (α), parts per million
| Material | α (µm/m·°C) | α (µin/in·°F) |
|---|---|---|
| Zinc | 30 | 16.7 |
| Lead | 29 | 16.1 |
| Magnesium | 25 | 13.9 |
| Aluminum | 23 | 12.8 |
| Brass | 19 | 10.6 |
| Bronze | 18 | 10.0 |
| Copper | 17 | 9.4 |
| Stainless steel (304) | 17 | 9.6 |
| Nickel | 13 | 7.2 |
| Carbon steel | 12 | 6.7 |
| Concrete | 12 | 6.7 |
| Cast iron | 11 | 6.1 |
| Glass (common) | 9 | 5.0 |
| Titanium | 8.6 | 4.8 |
| Glass (borosilicate) | 3.3 | 1.8 |
| PVC | 50 | 28 |
| HDPE | 120 | 67 |
These are linear coefficients (α): the fractional change in length per degree, in parts per million (multiply by 10 to the minus 6). To find growth, multiply α by the length and the temperature change. Plastics expand far more than metals, and dissimilar materials joined together can warp or loosen as temperatures swing.
Need conductivity instead of expansion?
See the Thermal Conductivity Chart, or browse the engineering calculators for a thermal expansion tool.
How to use the coefficient
Linear expansion equals alpha times the original length times the temperature change. A 1-meter aluminum bar, with alpha about 23 parts per million per degree C, heated 50 degrees grows by roughly 1.15 mm. Over long spans this adds up, which is why bridges and pipelines need expansion joints.
Why mismatched expansion matters
When two materials with different coefficients are bonded, heating builds stress at the joint because each wants to grow by a different amount. This drives bimetallic strips in thermostats, can crack glass-to-metal seals, and loosens press fits. Matching coefficients, or allowing for the difference, avoids trouble.
FAQ
What is the thermal expansion coefficient of steel?
About 12 parts per million per degree Celsius for carbon steel, or roughly 6.7 per degree Fahrenheit. Stainless is higher at about 17.
How much does aluminum expand compared to steel?
Aluminum expands about twice as much as steel for the same temperature change, near 23 versus 12 parts per million per degree Celsius.
How do I calculate thermal expansion?
Multiply the coefficient by the original length and the temperature change. The result is the change in length in the same units as the length.