Celsius vs Kelvin — which temperature scale is "correct"?
Same size, different zero. When to use Kelvin and when Celsius is fine.
Celsius is the everyday scale for weather, cooking, body temperature
Kelvin is the SI base; absolute zero at 0 K
Both scales are the same size (1 K = 1 °C in magnitude). They differ only in their zero point.
- 0 °C = 273.15 K (freezing point of water) - 0 K = absolute zero (−273.15 °C, where atomic motion stops)
When to use Celsius: weather, cooking, body temperature, swimming-pool temperatures, and any context where you'll see negative numbers in extreme cases but never need to compare to fundamental physics.
When to use Kelvin: thermodynamics, gas law calculations (PV = nRT), astronomical temperatures (the Sun is 5,778 K, not 5,505 °C), LED colour temperature, cryogenics.
The formula K = °C + 273.15 is exact. The reverse °C = K − 273.15 is exact. The two scales differ by exactly 273.15 everywhere.
The shift isn't a "translation" in the linguistic sense — it's an offset that's added (or subtracted) consistently. Hence temperature is an affine quantity on this site: the conversion is linear with an offset, not just multiplicative.
Frequently Asked Questions
Which should I use?
Use Celsius for everyday temperature, weather, cooking, body temperature.
When is the alternative better?
Use Kelvin for physics, chemistry, gas law calculations, and astronomical temperatures.
How is the conversion calculated?
Every conversion is a single factor (or an affine formula). The math is identical either direction; the difference is context.