Temperature Converter
Convert between Celsius, Fahrenheit, kelvin and Rankine.
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Temperature units
Every unit below converts to every other one in the calculator. Values are relative to the base unit, the kelvin (K).
| Unit | Symbol | System | Value |
|---|---|---|---|
| Kelvin | K | SI | Base unit |
| Degree Celsius | °C | SI | K = °C + 273.15 |
| Degree Fahrenheit | °F | US customary | K = (°F + 459.67) ÷ 1.8 |
| Degree Rankine | °R | US customary | K = °R ÷ 1.8 |
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About temperature units
Temperature scales do not all start at the same zero, so converting between them needs an offset as well as a factor. For example, °F = °C × 1.8 + 32.
Kelvin and Rankine are absolute scales: zero means absolute zero. A kelvin is the same size as a degree Celsius, and a degree Rankine is the same size as a degree Fahrenheit.
Useful reference points: water freezes at about 0 °C (32 °F, 273.15 K) and boils at about 100 °C (212 °F) at standard atmospheric pressure. A body temperature of 37 °C is 98.6 °F.
Frequently asked questions
- At what temperature are Celsius and Fahrenheit equal?
- At −40. −40 °C is exactly −40 °F.
- Why does this converter convert temperatures, not temperature differences?
- A reading of 10 °C converts to 50 °F, but a change of 10 °C is a change of 18 °F. This converter handles readings. To convert a difference, multiply by the ratio of degree sizes (1.8 between °C and °F).
- Is it "degrees kelvin"?
- No. Since 1967 the unit is simply "kelvin" (symbol K), without "degree".
- How can I estimate Fahrenheit from Celsius in my head?
- Double the Celsius value and add 30. For 20 °C that gives 70 °F; the exact value is 68 °F. The estimate gets worse for high temperatures, so use the converter when it matters.