Kelvin to Celsius is a straight subtraction; Fahrenheit takes one more step
Kelvin and Celsius degrees are the same size, so converting between them is just the fixed 273.15 offset. A change of 1 K is a change of 1 °C. Fahrenheit degrees are smaller, so the Kelvin value also gets scaled by 1.8 after the offset.
Fixed points across all three scales
| Kelvin | Celsius | Fahrenheit | What it is |
|---|---|---|---|
| 0 K | −273.15 °C | −459.67 °F | Absolute zero |
| 273.15 K | 0 °C | 32 °F | Water freezes |
| 293 K | ~20 °C | ~68 °F | Room temperature |
| 310 K | ~37 °C | ~98.6 °F | Body temperature |
| 373.15 K | 100 °C | 212 °F | Water boils |
| 5778 K | ~5505 °C | ~9940 °F | Surface of the Sun |
The cosmic microwave background, the coldest natural temperature in the universe, sits at about 2.73 K.
What trips people up
- No degree symbol. Kelvin is absolute, so it is 300 K, not 300°K. Only Celsius and Fahrenheit carry the °.
- Offset, not ratio. Doubling the Celsius reading does not double the Kelvin. Only differences convert cleanly; a 10 K rise is always a 10 °C rise.
- Precision matters. The offset is 273.15 exactly, not 273. Rounding to 273 shifts every scientific result by 0.15 K.
- Nothing below zero. Any negative Kelvin is a data error, not a valid temperature.
Common questions
How do I convert Kelvin to Celsius?
Subtract 273.15. So 300 K is 300 minus 273.15, which is 26.85 degrees Celsius. To go back the other way, add 273.15 to the Celsius value.
What is 0 Kelvin?
Zero Kelvin is absolute zero, the coldest temperature physically possible, where molecular motion stops. It equals minus 273.15 degrees Celsius and minus 459.67 degrees Fahrenheit. No Kelvin value can be negative.
Why write 300 K and not 300 degrees K?
Kelvin is an absolute unit, so it takes no degree symbol and no word degrees. You write 300 K, never 300 degrees K. Celsius and Fahrenheit still use the degree symbol.
