Rankine temperature scale, scale established in 1859 by Scottish engineer and physicist William John Macquorn Rankine (1820–72), with its zero set to the theoretical temperature at which the molecules of a substance have the lowest energy (absolute zero). The Rankine (°R) scale is the absolute temperature scale related to the Fahrenheit (°F) scale, and both scales have the same size unit of temperature. The two scales are related by the equation °R = °F + 459.67. The freezing point of water occurs at 491.67 °R, whereas its boiling point occurs at 671.67 °R.
The zero point of the Rankine scale matches that of the Kelvin scale, and the two scales are related by the equation °R = 1.8 × K. In certain fields of engineering, such as aerospace engineering, the Rankine scale is often preferred over the Kelvin scale with respect to absolute temperature.