Engineering Reference

Thermal Expansion Calculator

Compute how much a part grows or shrinks over a temperature change, for any material and length.

Page last changed 2026-10-19 · based on n/a — standard engineering relationships, no single governing revision

Quick Answer

ΔL = α × L × ΔT. A 1 m aluminium bar (α = 23.6 µm/m·°C) heated by 50 °C grows 1.18 mm; the same bar in steel (α = 11.7) grows 0.59 mm — about half as much.

Thermal Expansion

The Formulas Used

ΔL = α × L × ΔT
where α is the coefficient of linear thermal expansion, L the original length and ΔT the temperature change. Keep units consistent — with α in µm/m·°C, express L in metres for the answer in micrometres.

Getting α Right

Coefficients of linear thermal expansion are on the thermal expansion chart. Two things to watch: the coefficient itself varies with temperature, so the tabulated value is an average over a range; and for polymers it depends strongly on temperature and moisture, so a single figure is only a rough guide.

Where It Bites

The absolute expansion rarely matters — it is the difference between materials that causes problems. An aluminium housing on a steel shaft grows twice as far, so a clearance that is correct at 20 °C can close completely at 70 °C. Long pipe runs need expansion loops for the same reason.

Frequently Asked Questions

How do I calculate thermal expansion?
ΔL = α × L × ΔT — the coefficient multiplied by the original length and the temperature change. For a 1 m aluminium bar over 50 °C: 23.6 × 10⁻⁶ × 1000 × 50 = 1.18 mm.
What is the coefficient of thermal expansion of aluminium?
About 23.6 µm/m·°C for 6061 — roughly twice that of steel, which is why aluminium parts need more clearance and why mixed aluminium-steel assemblies change fit with temperature.
Does thermal expansion affect bolted joints?
Yes. A steel bolt in an aluminium housing loses preload as the assembly heats, because the aluminium expands away from the bolt. Where temperature swings are large this has to be accounted for in the preload specification.
How much does steel expand per degree?
About 11.7 µm per metre per degree Celsius — roughly 0.012 mm on a 1 m bar. A 50 °C rise gives about 0.59 mm.
Why does thermal expansion matter for long pipes?
A 30 m steel run at 80 °C grows about 25 mm, which will bow the pipe or overload the anchors if it is restrained. Expansion loops or joints absorb the movement.

Related

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

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Data Sources

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Formulas as shown on this pagen/a — standard engineering relationships, no single governing revisionevery value this calculator produces

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