Unit ofTemperature
SymbolR, °R, °Ra
Named afterMacquorn Rankine
x R in ...... corresponds to ...
   Kelvin scale   5/9x K
   Celsius scale   (5/9x − 273.15) °C
   Fahrenheit   (x − 459.67) °F

The Rankine scale (/ˈræŋkɪn/) is an absolute scale of thermodynamic temperature named after the University of Glasgow engineer and physicist Macquorn Rankine, who proposed it in 1859.[1]


Similar to the Kelvin scale, which was first proposed in 1848,[1] zero on the Rankine scale is absolute zero, but a temperature difference of one Rankine degree (°R or °Ra) is defined as equal to one Fahrenheit degree, rather than the Celsius degree used on the Kelvin scale. In converting from kelvin to degrees Rankine, 1 K = 9/5 °R or 1 K = 1.8 °R. A temperature of 0 K (−273.15 °C; −459.67 °F) is equal to 0 °R.[2]


The Rankine scale is still used in engineering systems where heat computations are done using degrees Fahrenheit.[3]

The symbol for degrees Rankine is °R[2] (or °Ra if necessary to distinguish it from the Rømer and Réaumur scales). By analogy with the SI unit, the kelvin, some authors term the unit Rankine, omitting the degree symbol.[4][5]

Some temperatures relating the Rankine scale to other temperature scales are shown in the table below.

Temperature Kelvin (K) Celsius (°C) Fahrenheit (°F) Rankine (°R)
Absolute zero 0 −273.15 −459.67 0
Freezing point of brine[a] 255.37 −17.78 0 459.67
Freezing point of water[b] 273.15 0 32 491.67
Boiling point of water[c] 373.1339 99.9839 211.97102 671.64102

See also


  1. ^ The freezing point of brine is the zero point of Fahrenheit scale, old definition, see: Grigull 1986
  2. ^ The ice point of purified water has been measured to be 0.000089(10) degrees Celsius – see Magnum 1995
  3. ^ For Vienna Standard Mean Ocean Water at one standard atmosphere (101.325 kPa) when calibrated solely per the two-point definition of thermodynamic temperature. Older definitions of the Celsius scale once defined the boiling point of water under one standard atmosphere as being precisely 100 °C. However, the current definition results in a boiling point that is actually 16.1 mK less. For more about the actual boiling point of water, see VSMOW in temperature measurement.


  1. ^ a b "Rankine". Merriam-Webster Dictionary. Retrieved 2019-11-07.
  2. ^ a b B.8 Factors for Units Listed Alphabetically from Thompson & Taylor 2008, pp. 45–69
  3. ^ Berger, Eric (2022-08-29). "Warning sign? NASA never finished a fueling test before today's SLS launch attempt". Ars Technica.
  4. ^ Pauken 2011, p. 20
  5. ^ Balmer 2011, p. 10