Kelvin (K)
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.
The kelvin is the reference unit for temperature on this site.
About the kelvin
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.
Sources: NIST: the kelvin and the SI redefinition; BIPM: 13th CGPM (1967), Resolution 3; Wikipedia: Kelvin
Kelvin conversion chart
100 kelvins expressed in every other temperature unit:
| Unit | 100 kelvins |
|---|---|
| Celsius | -173.15 |
| Fahrenheit | -279.67 |
| Rankine | 180 |
| Réaumur | -138.52 |
| Delisle | 409.725 |
| Newton | -57.1395 |
| Rømer | -83.40375 |
More Metric (SI) units
- degree Celsius (temperature)
- meter (length)
- kilometer (length)
- centimeter (length)
- millimeter (length)
- micrometer (length)
- nanometer (length)
- picometer (length)
- decimeter (length)
- hectometer (length)
- decameter (length)
- kilogram (weight & mass)
- gram (weight & mass)
- milligram (weight & mass)
- microgram (weight & mass)
- metric ton (weight & mass)
Browse all temperature units.