Comparison of the Fahrenheit, Celsius, and Kelvin scales. Credit: NASA .
The kelvin (K) is the base unit of thermodynamic temperature in the SI system of units. It is equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. One kelvin corresponds to an interval of one degree on the Celsius (centigrade) scale, so that the freezing and boiling points of water, at standard pressure, are 273 K and 373 K, respectively. The temperature of absolute zero is 0 K (-273.16°C). The unit is named after the Scottish physicist Lord Kelvin (William Thomson).