Convert Celsius to Kelvin

Celsius to Kelvin: K = °C + 273.15

To go from degrees Celsius to kelvin, add 273.15: K = °C + 273.15. Nothing gets multiplied, because one Celsius degree and one kelvin are the same size; only the starting point moves. Example: 20 °C + 273.15 = 293.15 K.

The converter on this page is already set to Celsius to Kelvin, starting from 20 °C. The answer updates as you type, rounded to six significant figures, and the "Formula:" line reads K = °C + 273.15. The ⇄ "Swap units" button turns it into Kelvin to Celsius. The "In every unit" table adds the Fahrenheit value, so 20 °C also shows as 68 °F. Type anything below −273.15 °C and a message tells you the temperature is below absolute zero and cannot exist.

Celsius to Kelvin conversion chart

Chemistry class, light bulbs, cryogenics

Gas laws. In PV = nRT, Charles's law and every AP or A-level gas problem, T must be in kelvin. Warm a sealed rigid can from 20 °C to 40 °C and the pressure does not double: it goes from 293.15 K to 313.15 K, a 6.82% rise. Plugging in Celsius is the classic mistake.

STP versus standard conditions. STP is defined at 0 °C, or 273.15 K, while thermodynamic tables are usually given at 25 °C, or 298.15 K. Check which one your problem means.

Light bulbs. A box marked 2700K "soft white" or 6500K "daylight" gives a color temperature, the hue of an object glowing at that temperature. An LED rated 2700K is not running at 2,426.85 °C.

Cryogenics. Liquid nitrogen boils at −195.8 °C, which is 77.35 K. Nothing goes below 0 K, so kelvin values are never negative.

Frequently asked questions

What is 0 °C in kelvin?

273.15 K. The triple point of water, 0.01 °C, is 273.16 K.

Is it "degrees Kelvin"?

No. Since 1967 the unit has been simply the kelvin, symbol K, with no degree sign: 300 K, said "300 kelvin" or "300 kelvins".

Does a change of 1 °C equal 1 K?

Yes. A rise of 5 °C is a rise of 5 K, which is why scientists often quote temperature differences in kelvin.