⚖️ Comparison · Updated for 2026
Celsius vs Kelvin
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
Quick answer: K = °C + 273.15. Kelvin is the SI temperature unit, used in science. The scales are the same size — a 1°C increase equals a 1 K increase — but they start from different zeros. 0 K is absolute zero; 0°C is the freezing point of water.
Decision guide — when to use which
Use Celsius when…
Everyday use everywhere outside the US, weather, cooking, body temperature.
Use Kelvin when…
All scientific work — physics, chemistry, engineering. Astronomy. Lighting (colour temperature, e.g. 'warm 2700K' bulbs).
📊 Side-by-side comparison
| 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.
Reviewed for 2026. All conversion factors and historical references verified against official sources (ISO standards, government weights & measures legislation, IEC technical specifications). Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project. We don't sell SEO links or accept paid placements in this content.