Kelvin (K)

Quantity: Temperature · Category: SI base

The kelvin is the SI base unit of thermodynamic temperature. Since 2019 it is defined by fixing the Boltzmann constant at exactly 1.380649×10⁻²³ joules per kelvin, so one kelvin is the temperature change that changes thermal energy by that amount per particle.

Relation to SI

Base unit — defined by k = 1.380649×10⁻²³ J/K (exact); 0 °C = 273.15 K

Examples

• Room temperature is about 293 K (20 °C).
• Water boils at 373.15 K at standard atmospheric pressure.
• Absolute zero, the coldest possible temperature, is 0 K.