Most solids get slightly longer when heated. The increase is proportional to the original length and to the temperature rise: ΔL = αL₀ΔT, where α is the coefficient of linear expansion of the material.
Choose a material or enter its α, then the length and temperature change. The answer is in millimetres and metres. It explains why railway tracks and bridges have expansion gaps.
| Material (α per °C) | Steel (12 × 10⁻⁶) |
| Original length (L₀) | 10 m |
| Temperature rise (ΔT) | 40 °C |
| Change in length (mm) | 4.8 |
| Change in length (m) | 0.0048 |
| New length (m) | 10.0048 |
The rail gets 4.8 mm longer, so tracks need small gaps between rails.
Try this example →| Material (α per °C) | Aluminium (23 × 10⁻⁶) |
| Original length (L₀) | 1,000 m |
| Temperature rise (ΔT) | 30 °C |
| Change in length (mm) | 690 |
| Change in length (m) | 0.69 |
| New length (m) | 1,000.69 |
The line lengthens by 690 mm, which is why power lines sag more in summer.
Try this example →ΔL = αL₀ΔT.
Per degree Celsius (/°C), the same as per kelvin (/K).
For solids, β ≈ 2α and γ ≈ 3α, so α : β : γ ≈ 1 : 2 : 3.
To give the rails room to expand in hot weather without buckling.