Kelvin to Celsius (K to °C)

1 kelvin equals -272.15 degrees Celsius.

How to convert kelvins to degrees Celsius

Converting kelvins to degrees Celsius is not a simple multiplication, so use the formula below.

°C = K − 273.15

Example: 10 kelvins = -263.15 degrees Celsius.

Temperature scales have different zero points, so converting is not just multiplication. Differences in degrees convert differently from absolute readings.

About these units

Kelvin (K)

Metric (SI)Current unit

The SI base unit of temperature. Zero kelvin is absolute zero, where particles have minimal thermal motion. A kelvin step is the same size as a Celsius degree.

Lord Kelvin, born William Thomson, published an absolute temperature scale in 1848 and refined it with James Joule in 1854. Its zero sits at absolute zero, and its degree is the same size as a Celsius degree. The kelvin entered the SI in 1954, defined as 1/273.16 of the thermodynamic temperature of the triple point of water, where ice, liquid and vapor coexist. In 1967 the 13th CGPM renamed the unit from the degree Kelvin to simply the kelvin, with symbol K, and no word degree.

Since 20 May 2019 the kelvin has been defined by fixing the Boltzmann constant at exactly 1.380649 times 10 to the minus 23 joule per kelvin, which frees it from the properties of any one substance. Scientists use it for stars and cryogenics, and lighting designers use it for color temperature. NIST notes that incandescent bulbs run near 3,000 K, daylight lamps at 5,000 to 5,600 K, and the Sun's surface at about 5,800 K. Room temperature, about 21 degrees Celsius, is roughly 294 K.

The kelvin is the reference unit for temperature on this site.

Sources: NIST: the kelvin and the SI redefinition; BIPM: 13th CGPM (1967), Resolution 3; Wikipedia: Kelvin

Degree Celsius (°C)

Metric (SI)Current unit

The metric temperature scale used worldwide for weather and daily life: water freezes at 0 °C and boils at 100 °C at standard pressure. Named after Anders Celsius.

Anders Celsius, a Swedish astronomer, proposed a scale in 1742 that ran the opposite way from the one we use: 0 for the boiling point of water and 100 for its freezing point. Credit for flipping it is shared and partly disputed. French physicist Jean-Pierre Christin published a reversed mercury thermometer in 1743, Carl Linnaeus is usually credited with reversing it in 1744, the year Celsius died, and others in Sweden, including Pehr Elvius, Daniel Ekström and Mårten Strömer, are also named as independent developers.

For much of the nineteenth century the scale was called centigrade, until the CGPM and CIPM adopted the name degree Celsius in 1948, partly to honor Celsius and to avoid confusion with a French term for a subdivision of the gradian. From 1954 to 2019 it was defined through absolute zero and the triple point of water; since 2019 it is tied to the Boltzmann constant. Strictly, water boils at about 99.974 degrees on the modern international temperature scale, not exactly 100. Australian weather reports switched exclusively to Celsius in 1972.

0 degrees Celsius = 273.15 kelvins (exactly).

Sources: Wikipedia: Celsius; BIPM: 9th CGPM (1948), Resolution 7; NIST: the kelvin and the SI redefinition

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