Kelvins to degrees Celsius converter

How to convert Kelvin to Celsius

Subtract 273.15 from the kelvin value: °C = K − 273.15. So 300 K = 26.85 °C, 273.15 K = 0 °C and 373.15 K = 100 °C, roughly where water boils at sea level.

Why the offset is exactly 273.15

A kelvin and a degree Celsius are the same size, so the two scales differ only in where zero sits. Zero kelvin is absolute zero, which is −273.15 °C.

The SI defines the Celsius temperature as the kelvin temperature minus 273.15, so the conversion is exact and involves no rounding (NIST).

Worked examples

Liquid nitrogen boils at about 77 K at sea-level pressure: 77 − 273.15 = −196.15 °C, or roughly −196 °C.

Physics problems often use 293.15 K or 298.15 K as room temperature: 293.15 − 273.15 = 20 °C, and 298.15 − 273.15 = 25 °C.

Kelvin to Celsius chart

0 K is absolute zero and 273.15 K is the freezing point of water. Any reading below 273.15 K gives a negative Celsius value, which is normal.

Temperature differences need no offset

Because the units are the same size, a change of 1 K equals a change of 1 °C. Warming from 293.15 K to 298.15 K is a rise of 5 K, which is also a rise of 5 °C.

Subtract 273.15 only from a reading. Subtracting it from a difference turns a 5 K rise into a meaningless −268.15 °C.

Common mistakes

• Using 273 instead of 273.15. Every answer comes out 0.15 °C too high: 300 K would read 27 °C instead of 26.85 °C.
• Writing "degrees kelvin" or °K. Since 1967 the unit has been the kelvin, symbol K, with no degree sign.
• Comparing ratios in Celsius. 300 K is double 150 K on the absolute scale, but their Celsius values are 26.85 °C and −123.15 °C. Ratios only make sense in kelvins.
• Reading a bulb's color temperature as heat. A 2,700 K light bulb describes the color of its light, not how hot the bulb is, so converting it to Celsius is not useful.

When you need kelvins instead

Gas laws and most physics formulas need absolute temperature. In PV = nRT, T must be in kelvins, so convert a Celsius lab reading before using it and convert the answer back for reporting.

For the reverse step, use the Celsius to Kelvin converter. To go from kelvins to Fahrenheit, use the Kelvin to Fahrenheit converter, and for Rankine or Réaumur, the temperature converter.