Thermal Expansion Converter: 1/K, 1/°C, 1/°F & More
Convert coefficient of thermal expansion (α)—fractional length change per degree—between SI, Fahrenheit, Rankine, and Reaumur.
Convert thermal expansion coefficient between 1/K, 1/°C, 1/°F, 1/°R, and 1/°r. Used for pipes, rails, composites, and stress analysis. Five units; all conversions use the SI base 1/K.
What is the coefficient of thermal expansion?
The coefficient of thermal expansion (α) is the fractional change in length per degree of temperature change. If a rod stretches by 0.001 (0.1%) when heated 1 K, α = 0.001 per K, or 1/K in SI. It’s “length per length per temperature,” so the unit is 1/K (or 1/°C, 1/°F, etc.). Materials with high α expand more for the same ΔT—important for joints, rails, and anything that sees temperature swings.
Where ΔL is the length change, L is original length, and ΔT is the temperature change. 1/°C and 1/K are the same size. 1/°F and 1/°R are 1.8× larger than 1/K (one Fahrenheit degree is smaller than one Celsius degree). Reaumur: 1/°r = 0.8× 1/K.
How conversion works
Every unit is converted via the SI base 1/K. Multiply your value by the source factor (e.g. 1/°F → 1.8 to get 1/K), then divide by the target factor to get the result. So 1 per °F = 1.8 per K; 1 per °r = 0.8 per K. The tool above does this for all five units.
Key units and when to use them
1/K or 1/°C
Factor: 1 (SI base)
Standard in SI and most engineering. Same numerical value for 1/K and 1/°C because one °C equals one K as an interval.
1/°F or 1/°R
Factor: 1.8 (to get 1/K)
US and imperial specs sometimes give α per °F. One °F is 5/9 K, so one per °F = 1.8 per K.
Who uses this converter?
Civil and mechanical engineers need α in consistent units for expansion joints, pipelines, and rail. Materials and packaging use it for composites and layered structures. Students see 1/K in textbooks but may find US datasheets in 1/°F. Converting to a common base (1/K) avoids errors in ΔL = α·L·ΔT. All conversions run in your browser.
Common conversions at a glance
| From | To | Formula |
|---|---|---|
| 1/°F | 1/K | × 1.8 |
| 1/°r | 1/K | × 0.8 |
Thermal Expansion FAQ
? Why is 1/°F equal to 1.8 per K?
One Fahrenheit degree is 5/9 of a kelvin (smaller step). So a coefficient given “per °F” means each smaller step; to express the same physical expansion per kelvin you need more units: 1 per °F = 9/5 = 1.8 per K.
? What is a typical thermal expansion coefficient?
Metals are often in the 10⁻⁵ to 2×10⁻⁵ per K range (e.g. steel ~12×10⁻⁶/K). Plastics can be 5–10× higher. Use this converter when your datasheet is in 1/°F or 1/°r and your calculation is in 1/K.
? How do I convert thermal expansion coefficient from 1/°F to 1/K?
Multiply by 1.8. So 1 per °F = 1.8 per K (because 1 °F = 5/9 K, so 1/°F = 9/5 per K). Use the converter for 1/°C, 1/°R, 1/°r (Reaumur) and to match US vs SI datasheets.
? What is linear thermal expansion coefficient used for?
It describes how much a material lengthens per degree of temperature change: ΔL/L = α·ΔT. Used in structures, piping, rails, and precision parts where temperature swings matter. Coefficients are often given in 1/K or 1/°C; US sources may use 1/°F—this tool converts between all supported units.
? What is the thermal expansion coefficient of steel in 1/K or 1/°F?
Carbon steel is about 11–13×10⁻⁶ per K (or per °C). In 1/°F that’s about 6.1–7.2×10⁻⁶ per °F. Use this converter to express any material’s α in 1/K, 1/°C, 1/°F, 1/°R, or 1/°r for consistent formulas.
? What is degree Rankine (°R) for thermal expansion?
Rankine is an absolute temperature scale with degree size equal to Fahrenheit (1 °R = 1 °F as an interval). So 1/°R = 1/°F for expansion coefficients. This converter includes 1/°R and 1/°r (Reaumur) for completeness when matching older or specialty sources.