Kelvin (K)
The kelvin (K) is the SI base unit of thermodynamic temperature. Zero kelvin is absolute zero; it is written without a degree sign.
Symbol: K
Quantity: thermodynamic temperature
SI relation: K is the coherent SI unit of temperature.
Derivation: SI base unit, fixed by the Boltzmann constant k = 1.380649 × 10⁻²³ J/K
Exact: yes, by definition
History
Named after William Thomson, Lord Kelvin. Since 2019 it is defined by fixing the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K.
Typical uses
- Physics, chemistry and gas-law calculations (PV = nRT)
- Cryogenics (liquid nitrogen 77 K, liquid helium 4.2 K)
- Colour temperature of lighting (2700–6500 K)
Convert kelvins to other units
| Conversion | 1 K equals | Reverse |
|---|---|---|
| Kelvin to Celsius | -272.15 °C | Celsius to Kelvin |
| Kelvin to Fahrenheit | -457.87 °F | Fahrenheit to Kelvin |
| Kelvin to Rankine | 1.8 °R | Rankine to Kelvin |
Open the Temperature Converter to convert any value between all units.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Section 2.3.1, base unit definitions.
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Kelvin (K). Retrieved October 17, 2026, from https://scientificconverters.com/units/kelvin/
IEEE
Scientific Converters, "Kelvin (K)," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/kelvin/