Thermal Expansion Calculator
Enter material, length and temperature swing to get the growth — the number expansion loops, pipe guides and bridge joints exist to absorb.
Last updated: 2026-09-28
How the calculation works
- Linear growth is proportional to length, temperature swing and the material's α coefficient.
- Outputs in mm and inches for both metric and imperial detail work.
- The percentage row shows why short parts ignore expansion while long runs cannot.
Formula
ΔL = α · L · ΔT
| Symbol | Meaning | Unit |
|---|---|---|
α | Linear expansion coefficient | ×10⁻⁶/°C |
ΔL | Length change | mm |
Worked example
Interpreting the result
Expansion is invisible until it binds: pipe guides seized by friction turn an 18 mm growth into buckling, and a bridge joint with no gap turns heat into cracked concrete. Design absorbs it three ways — expansion loops (let it flex), sliding guides (let it slide), or expansion joints (cut the run). Aluminum moving 2× steel is why aluminum skins on steel frames need slotted holes.
Assumptions
- Room-temperature α coefficients; varies a few percent over wide ranges.
- Unrestrained member — real anchor and guide stiffness change the stress picture.
Limitations
- Computation of induced stress (from restraint) is not included — restrained thermal strain needs σ = E·α·ΔT.
- Anisotropic materials (wood) differ along grain vs across.
Frequently asked questions
How much does steel expand per degree?
12 microns per metre per °C — a 30 m run grows 0.36 mm per °C. Over a 50 °C swing that is 18 mm of movement to accommodate.
Why do pipes need expansion loops?
The pipe will move whether or not you plan for it: unrestrained growth bends things, restrained growth builds stress (E·α·ΔT — hundreds of MPa). Loops let the pipe flex within safe stress.