Thermal Expansion Calculator

This thermal expansion calculator uses the expansion coefficient, the length and the temperature difference: a 10 m steel bar heated from 20 to 80 °C grows by 7.2 mm.

Example: What do you want to calculate: Change in length · Material: Steel (12 · 10⁻⁶/K) · Initial length 10 m · Starting temperature 20 °C · Final temperature 80 °C → Result: Change in length ΔL = +7.2 mm, new length 10.0072 m. Source: Wikipedia – Wärmeausdehnung (coefficient of linear and volumetric expansion). Updated: 2 October 2026.

What do you want to calculate?

Material

Initial length

Starting temperature

°C

Final temperature

°C

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Result

Result: Change in length ΔL = +7.2 mm, new length 10.0072 m
Calculation values: Item Value
Linear expansion coefficient α 12 · 10⁻⁶ / K
Temperature change ΔT 60 K
Change in length ΔL +7.2 mm
Relative change +0.072 %
New length 10.0072 m
Expansion per metre or percent: Temperature change Change in length per metre
10 K 0.12 mm
20 K 0.24 mm
50 K 0.6 mm
100 K 1.2 mm; The coefficients are guide values at about 20 °C and hold for a small temperature range; alloys, concrete mixes and plastics vary with their recipe. For contracts and components the manufacturer's data applies.

Item	Value
Linear expansion coefficient α	12 · 10⁻⁶ / K
Temperature change ΔT	60 K
Change in length ΔL	+7.2 mm
Relative change	+0.072 %
New length	10.0072 m

Temperature change	Change in length per metre
10 K	0.12 mm
20 K	0.24 mm
50 K	0.6 mm
100 K	1.2 mm

How it is calculated

Solids expand when heated: the change in length is ΔL = α · L₀ · ΔT with the linear expansion coefficient α, the initial length L₀ and the temperature change ΔT. On cooling ΔT is negative and the body gets shorter.

Length, area and volume

Length grows in proportion to α, area roughly with 2α and volume with γ ≈ 3α. A 10 m steel bar (α = 12 · 10⁻⁶ / K) heated by 60 K expands by 12 · 10⁻⁶ · 10 · 60 = 0.0072 m, that is 7.2 mm. Aluminium at 23.1 expands almost twice as much as steel, and plastics such as HDPE by a factor of 15 to 20.

Where it matters

Pipework, rails, bridges, facades, fences and underfloor heating need expansion joints or loops, otherwise stresses and cracks appear. In engineering fits, thermal expansion decides whether a shrink fit holds.

The table shows the expansion per metre for 10, 20, 50 and 100 K.
Choose “Custom value” if your material is not in the list.
Liquids and gases have other, strongly temperature-dependent coefficients.

Frequently asked questions

How do you calculate thermal expansion?

ΔL = α · L₀ · ΔT. For 10 m of steel (α = 12 · 10⁻⁶ / K) and 60 K that gives 7.2 mm.

How much does a plastic pipe expand?

PVC-U expands by about 0.08 mm per metre and kelvin, HDPE by about 0.2 mm. A 10 m HDPE pipe grows by 80 mm over 40 K.

What is the difference between α and γ?

α describes the change in length, γ the change in volume. For uniform solids γ ≈ 3α.

Sources and legal basis

As of: 2 October 2026 · Editorial policy