Celsius vs Kelvin
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
Everyday use everywhere outside the US, weather, cooking, body temperature.
All scientific work — physics, chemistry, engineering. Astronomy. Lighting (colour temperature, e.g. 'warm 2700K' bulbs).
| Aspect | Celsius | Kelvin |
|---|---|---|
| Zero point | Water freezing | Absolute zero (-273.15°C) |
| Symbol | °C | K (no degree sign) |
| Scale size | Same as Kelvin | Same as Celsius |
| Room temperature | 20°C | 293 K |
Frequently asked
Why don't Kelvin temperatures have a degree symbol?
By international convention since 1968, kelvin is treated like any other SI unit — 'one kelvin' not 'one degree kelvin'. The degree symbol was officially dropped at the 13th General Conference on Weights and Measures.
What's negative in Kelvin?
Nothing. Kelvin starts at absolute zero — the coldest possible temperature — so there are no negative kelvin values in normal physics.
Frequently asked questions
Why don't Kelvin temperatures have a degree symbol?
By international convention since 1968, kelvin is treated like any other SI unit — 'one kelvin' not 'one degree kelvin'. The degree symbol was officially dropped at the 13th General Conference on Weights and Measures.
What's negative in Kelvin?
Nothing. Kelvin starts at absolute zero — the coldest possible temperature — so there are no negative kelvin values in normal physics.