Engineering Reference

Thermal Expansion Calculator

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

Data verified 2026-09-29 · 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

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#SourceTypeRevision / method
[1]ASME B1.1 — Unified Inch Screw ThreadsstandardASME B1.1-2019 — source
[2]ASTM A615 — Deformed steel bars for concrete reinforcementstandardASTM A615/A615M-20 — source
[3]ASTM E140 — Hardness Conversion TablesstandardASTM E140-12b — source
[4]Values computed in your browserderivedEvaluated locally from the formulas shown on the page. No data leaves the device.
[5]ISO 4287 — Surface texture: Profile methodstandardISO 4287:1997 — source
[6]ISO 68-1 — Basic profilestandardISO 68-1:2023 — source
[7]NFPA 70 NEC Table 310.16standardNEC 2023 (NFPA 70-2023) — source

Data Sources

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

Cross-checked against:

Derived values — the following values on this page are calculated, not taken directly from the standard:

ValueHow it is derived
All outputsComputed in the browser from the formulas above. No data leaves the device.

Outputs are computed from the formulas shown. Verify against the governing standard for design or acceptance work.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.