Celsius to Kelvin

Kelvin is the temperature unit of physics and chemistry, and the conversion from Celsius is the gentlest in this whole catalogue: the degrees are the same size, so only the starting point changes. Add 273.15 and you are done.

How it is calculated

K = °C + 273.15

A change of one degree Celsius is a change of exactly one kelvin, which is why temperature differences need no conversion at all. Only absolute temperatures do. Note that kelvin takes no degree sign and no plural — it is 300 K, never 300 °K and never 300 kelvins.

Source: NIST SP 811 (2008), Appendix B.8 — degree Celsius (°C) to kelvin (K): T/K = t/°C + 273.15

Common values

Questions people ask

Why does Kelvin start at −273.15 °C?

Because that is absolute zero — the point where the thermal motion that temperature measures reaches its minimum. There is nothing below it, which is what makes the scale useful: ratios mean something. 600 K really is twice as hot as 300 K, while 60 °C is not twice 30 °C.

Do I convert a temperature difference too?

No. A rise of 10 °C is a rise of 10 K, full stop. The offset cancels when you subtract, which is why heat calculations can use either unit as long as they use differences rather than absolute values.

Where will I actually meet kelvin?

Gas laws, thermodynamics, and the colour temperature of light — a warm bulb is around 2700 K and daylight about 6500 K. That last use is a different measure of the same physics: the temperature a glowing body would need to emit that colour.

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