Open measurement reference
Temperature scale conversion
A compact reference for converting Celsius, Fahrenheit, kelvin and Rankine while preserving the offset as well as the scale.
Temperature calculator
Why temperature is different
Most unit conversions need only a multiplier. Temperature scales also have different zero points, so they require an affine transform: apply both an offset and a scale factor. Multiplying 20 °C by 9/5 without adding 32 is therefore incorrect.
Direct formulas
| Conversion | Formula | Reference check |
|---|---|---|
| Celsius to kelvin | K = °C + 273.15 | 0 °C = 273.15 K |
| Kelvin to Celsius | °C = K − 273.15 | 273.15 K = 0 °C |
| Celsius to Fahrenheit | °F = °C × 9/5 + 32 | 100 °C = 212 °F |
| Fahrenheit to Celsius | °C = (°F − 32) × 5/9 | 32 °F = 0 °C |
| Kelvin to Rankine | °R = K × 9/5 | 273.15 K = 491.67 °R |
| Rankine to kelvin | K = °R × 5/9 | 0 °R = 0 K |
Worked check
To convert 68 °F to Celsius, subtract 32 to obtain 36, then multiply by 5/9. The result is 20 °C. Reversing the calculation gives 20 × 9/5 + 32 = 68 °F, confirming the transform.
Absolute zero and temperature intervals
Absolute zero is 0 K, −273.15 °C, 0 °R and −459.67 °F. Temperature differences do not use the zero-point offset: a change of 1 °C equals a change of 1 K, while a change of 1 °F equals a change of 1 °R and 5/9 K.
Precision guidance
Keep the exact fractions 9/5 and 5/9 during calculation, and round only the reported result. Do not write a degree symbol with kelvin: the unit name is kelvin and the symbol is K.
More temperature conversions
For additional scales, localized definitions and quick calculations, use the UnitConv temperature converter.