Kelvin to Celsius

Physics and chemistry state temperatures in kelvin, and this direction turns such a figure back into the scale an ordinary thermometer shows. The two scales share a degree size, so nothing is stretched: subtract 273.15 and the number is in Celsius. What does change is the sign. Kelvin counts up from absolute zero, so every temperature below 273.15 K becomes a negative Celsius value.

How it is calculated

°C = K − 273.15

This is the relation exactly as NIST prints it. The 273.15 is not a rounded measurement but the definition of the Celsius scale — Celsius temperature is thermodynamic temperature less 273.15 K — so the conversion is exact. There is no multiplier, because a kelvin and a degree Celsius are the same size.

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

Common values

Questions people ask

What is 0 K in Celsius?

−273.15 °C. Zero kelvin is absolute zero, where the thermodynamic scale starts. Everything below 273.15 K is negative in Celsius, which is why a winter day at −10 °C still reads as a large positive number, 263.15 K, on the kelvin scale.

Why subtract 273.15 and not 273?

Because 273.15 is fixed by definition, not rounded from a measurement. NIST SP 811 defines Celsius temperature as t = T − T0 with T0 = 273.15 K, so the decimals are part of the relation. Subtracting 273 leaves every result 0.15 °C too warm.

Does a temperature difference in kelvin need converting?

No. The kelvin and the degree Celsius are the same size, so the offset cancels when you subtract. NIST illustrates it with the gap between the freezing point of gallium and the triple point of water: 29.7546 K, which is also 29.7546 °C. Only absolute temperatures need the 273.15.

How do I get from kelvin to Fahrenheit?

Subtract 273.15 to reach Celsius, then multiply by 1.8 and add 32. NIST lists the opposite direction as T/K = (t/°F + 459.67)/1.8, which puts absolute zero at −459.67 °F.

Related tools