Convert Celsius to Kelvin

About converting Celsius to Kelvin

Celsius (°C) and Kelvin (K) are different temperature scales, so they convert with a formula rather than a simple ratio: K = °C + 273.15. That is why 100 Celsius is 373.15 Kelvin but 1 Celsius is 274.15 Kelvin — the scales have different zero points, so you cannot just multiply.

What is a Celsius?

Anders Celsius proposed his scale in 1742 with the numbers running backwards: 0 marked the boiling point of water and 100 its freezing point. It was inverted to the familiar arrangement shortly after his death. The unit was called centigrade until 1948, when the international body governing measurement settled on Celsius instead, partly because "grade" already meant a different thing in French. The scale is no longer defined by water at all — it is derived from the kelvin, offset by 273.15, with the curious result that water’s boiling point now falls a fraction below a tidy 100.

What is a Kelvin?

Unlike the other temperature scales, the kelvin starts at the true bottom of the range: absolute zero, the point at which thermal motion is minimal. Because nothing can be colder there are no negative kelvins, and by convention no degree symbol either — it is "300 kelvin", never "300 degrees Kelvin". It is the SI base unit of thermodynamic temperature, named for William Thomson, Lord Kelvin, who took his title from the river running through Glasgow, and it was redefined in 2019 in terms of the Boltzmann constant. Most people meet it unknowingly when buying light bulbs, where colour temperature is quoted in kelvin.

To put both in perspective: water freezes at 0 degrees Celsius, while room temperature is about 293 kelvin.

The converter above updates as you type, and the table lists common values for quick reference. Need the opposite direction? Use the Kelvin to Celsius converter, or browse all Temperature converters.