Thermal Expansion Calculator
How much a part grows or shrinks with temperature: length change, shaft/hole diameter growth, and the expansion gap to leave — with a material library that fills in the coefficient for you.
What Is Thermal Expansion?
Almost every material grows when it heats up and shrinks when it cools. For a solid the length change is steady and predictable:
where α is the coefficient of linear thermal expansion, L the original length and ΔT the temperature change. The effect is tiny per degree but adds up fast over long runs and wide temperature swings — which is exactly why expansion joints, slotted holes and clearance gaps exist.
Three Ways to Use It
Linear expansion gives the length change and final length of a part — the default mode. Diameter expansion handles shafts, holes, bearings and press fits, where even a few thousandths matters. Expansion gap turns a run length and a temperature range into the gap you should leave for rails, decking, siding, flooring or pipe.
Coefficient of Thermal Expansion Table
Typical linear expansion coefficients the material library auto-fills (µm/m·°C, i.e. parts per million per °C):
| Material | α (µm/m·°C) |
|---|---|
| HDPE | 150 |
| PVC | 50 |
| Aluminum 6061 | 23.6 |
| Aluminum 6063 | 23.4 |
| Brass | 19 |
| Stainless 304 | 17.3 |
| Copper | 16.5 |
| Stainless 316 | 16 |
| Steel | 12 |
| Concrete | 10 |
| Glass | 9 |
Where It Comes Up
- Mechanical design — clearances and fits that must hold across a temperature range.
- Structural & civil — expansion joints in bridges, rails and concrete.
- Piping — expansion loops and joints sized from run length and ΔT.
- HVAC — duct and pipe growth in heating and cooling.
- Manufacturing & machining — part dimensions at temperature vs at the gauge bench.
- Lighting fixtures — aluminum extrusions and lenses that move as LEDs heat them.
Frequently Asked Questions
Why is the expansion so small?
Coefficients are in parts per million per degree. A steel bar only grows about 0.0012 percent per °C — but over 20 m and 60 °C that is roughly 14 mm, more than enough to buckle a fixed run.
Shaft in a hole — what about clearance?
Both parts expand. The clearance change is the difference between the hole growth and the shaft growth, so matching materials keep fits stable while mismatched materials can bind or loosen.
Does the gap need a safety factor?
The calculator gives the theoretical expansion. Designers usually add margin for installation tolerance and temperature extremes beyond the stated range.
Thermal expansion resources
- Expansion coefficient table (above)
- Material property database
- Common expansion-joint guidelines
- Pipe expansion charts
Related calculators
- Heat Transfer Calculator — conduction, convection and the temperatures that drive expansion.
- Material Weight Calculator — mass of the same parts and stock.
- Stress Calculator — thermal stress when expansion is constrained.
- Beam Deflection Calculator — another serviceability check.