Kelvin (°K)

The kelvin (symbol: K) is the SI base unit of thermodynamic temperature, named after the physicist William Thomson, Lord Kelvin. The scale begins at absolute zero, the theoretical state where particles possess minimal thermal energy. Historically anchored to the triple point of water, the kelvin was redefined in 2019 by fixing the numerical value of the Boltzmann constant, eliminating reliance on material standards and aligning temperature measurement with fundamental physics.