Thermal Expansion Calculator
Calculate how much a part grows or shrinks with temperature — change in length, final length, linear strain and volumetric change — from a built-in library of 36 material expansion coefficients, in Celsius or Fahrenheit.
Input
Supplies the linear expansion coefficient. Pick “Custom” to type your own.
Only used when the material is “Custom”, or to override the library value.
A final temperature below the initial one gives a negative result — contraction rather than expansion.
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
What this calculator does
It works out how much a part changes size when its temperature changes — the difference between a shaft that slides into its housing and one that seizes. Give it a material, a starting length and two temperatures and it returns the change in length, the final length, the linear strain, and the approximate volumetric change.
The change in length is reported in your chosen unit and in millimetres and inches, because clearance decisions are usually made in whichever unit the drawing is not in.
The formula
Free (unconstrained) linear expansion:
ΔL = α × L₀ × ΔT
L₁ = L₀ + ΔL
- α is the coefficient of linear thermal expansion, in 10⁻⁶ per °C
- L₀ is the original length
- ΔT is the temperature change
Strain is ΔL / L₀, and volumetric change is approximately 3 × α × ΔT — the standard approximation that holds comfortably while α × ΔT stays small, which covers essentially every engineering temperature range.
How to use it
- Pick the material. The list carries 36 coefficients — metals, plastics, glass, masonry and a few outliers like Invar and fused quartz — so you don't have to look one up.
- Enter the original length and its unit (mm, cm, m, in or ft).
- Choose Celsius or Fahrenheit, then enter the initial and final temperatures.
- To use your own coefficient, pick Custom and type it in the α field. Typing a value while a named material is selected overrides the library figure for that run.
Why does a Fahrenheit range give a different answer than the same number in Celsius?
Because a Fahrenheit degree is smaller. The coefficients are per Celsius degree (identical to per Kelvin), so a Fahrenheit temperature span is scaled by 5/9 before it is used. A 40 °F rise is a 22.2 °C rise, and expands the part accordingly.
Can I use this to size a press fit or an interference fit?
For the heating or chilling step, yes — that is exactly the free-expansion case this calculates, and it tells you how much a hub grows when heated or a shaft shrinks in dry ice. What it does not give you is the stress once the parts are assembled and the expansion is constrained; that needs the material's elastic modulus and a press-fit calculation.
Why is the coefficient only valid near room temperature?
α is not really a constant — it drifts with temperature, and for some materials (polymers near their glass transition, steels through a phase change) it drifts sharply. The values here are the standard near-20 °C figures. For cryogenic work or anything above a few hundred degrees, use a mean coefficient taken over your actual temperature range.
Does a negative result mean something is wrong?
No — a final temperature below the initial one produces a negative ΔL, which is contraction. The final length is correspondingly shorter.
Privacy
Every calculation runs in your browser. Nothing about your materials, dimensions or design is uploaded.
Related tools
To convert between temperature scales on their own, use the Temperature Converter; for the length units this tool doesn't list, the Length Converter covers the rest.