Celsius to Kelvin

Degrees Celsius and kelvins

The Celsius scale is defined from the kelvin: t/°C = T/K − 273.15, so water freezes at about 0 °C and boils at about 100 °C at sea level. Weather, cooking and body temperature are given in Celsius almost everywhere except the United States.

The kelvin is the SI base unit of thermodynamic temperature, starting at absolute zero; since 2019 it is defined by fixing the Boltzmann constant. Science and engineering use kelvins, as do color temperatures of light bulbs and screens (2700 K warm, 6500 K daylight).

Worked example

Convert 25 °C with K = °C + 273.15: the result is 298.15 K. Likewise 10 °C = 283.15 K.

Estimating in your head

Add 273, or 273.15 for exact work: 25 °C is about 298 K.

Going the other way

To convert kelvins to degrees Celsius, type in the right-hand box; the page solves the same formula backwards. The swap button between the boxes opens the reverse page.

K = °C + 273.15

Temperature scales have different zero points as well as different degree sizes, so the conversion scales and shifts; there is no single factor. The page converts through kelvin using the exact definitions in NIST SP 811. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.