The kelvin (symbol: K) is a unit of measurement for temperature. It is named after the London engineer and physicist William Thomson, who was elevated to the peerage as Lord Kelvin in 1892, four years after his death. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin unit is equal to one quadrant of the thermodynamic temperature scale (at least in theory), which ranges from zero to a maximum value of plus and minus 273.15 degrees. The Kelvin scale is widely used in science and technology. The Kelvin temperature unit is used as a measure of absolute temperature. It's the equivalent of 0° Celsius and 273.15 K (degrees Kelvin) equals -273.15° Celsius, or 0° Kelvin is equal to the triple point of VSMOW (standard mean ocean water). There are several combinations and conversions of units that involve the Kelvin temperature. To convert between Fahrenheit and Celsius using kelvins, you must add 273.15 to a number in Fahrenheit to get its value in kelvins. For example, adding 273.15 to 212 degrees Fahrenheit will give you about 373.15 kelvins.

The rankine temperature unit, also known as the absolute thermodynamic temperature scale, is a non-SI metric unit of measurement for temperature. It is used in a variety of engineering contexts and usually expressed in kelvins (K). The Rankine scale was invented by the Scottish engineer William John Macquorn Rankine. Rankine temperature is a heat energy in British and American units of measurement. It is used extensively in the steam power industry, as it is suitable for working with saturated steam. The Rankine temperature scale was created by the Scottish engineer and physicist William John Macquorn Rankine (1820-1872). He set absolute zero at -459.67 °F (-273.15 °C) and the boiling point of water at 707.2 °F (374.6 °C). This means that a 1:1 mixture of water and ice has a temperature of 32°F (0°C), while a 1:1 mixture of steam and water has a temperature of 212°F (100°C).