Kelvin
The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By definition, the units of the Celsius scale (symbol °C) and the Kelvin scale have the same magnitude (that is, a rise in temperature of one kelvin and a rise of 1 °C are both equal to 1 K), and any temperature in degrees Celsius can be converted to the kelvin scale by adding 273.15.