This article is about the temperature scale. For the idealized thermodynamic cycle for a steam engine, see Rankine cycle. For the scale measuring recovery after stroke, see Modified Rankin Scale.
Rankine
QuantityTemperature
NamedafterW. J. M. Rankine
Convertfromxyes
Calcinput491.67
Units 1Kelvin
Inunits 1273.15 K
Units 2Celsius
Inunits 20.00 °C
Units 3Fahrenheit
Inunits 332.00 °F

The Rankine scale (/ˈræŋkɪn/ RANG-kin) is an absolute scale of thermodynamic temperature named after the University of Glasgow engineer and physicist W. J. M. 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, 5//9 K R  =  or 1 K (1.8 °R). A temperature of 0 K (−273.15 °C; −459.67 °F) is equal to 0 °R.[2][3]

Usage

The Rankine scale is used in engineering systems where heat computations are done using degrees Fahrenheit.[4]

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 kelvin, some authors term the unit Rankine, omitting the degree symbol.[5][6]

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

Scale
KelvinRankineFahrenheitCelsiusRéaumur
TemperatureAbsolute zero0 K0.00 °R; −459.67 °F; −273.15 °C−218.52 °Ré
Freezing point of brine[a]255.37 K459.67 °R; 0.00 °F; −17.78 °C−14.22 °Ré
Freezing point of water[b]273.15 K491.67 °R; 32.00 °F; 0.00 °C0 °Ré
Boiling point of water[c]373.1339 K671.641 °R; 211.971 °F; 99.9839 °C79.9871 °Ré

See also

Notes

  1. ^ The freezing point of brine is the zero point of Fahrenheit scale, old definition.[7]
  2. ^ The ice point of purified water has been measured to be 0.000089 degrees Celsius.[8]
  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 degC. 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.[citation needed]

References

  1. ^ Retrieved 2019-11-07.
  2. ^ Thompson, Ambler & Taylor, Barry N. (2008). "Guide for the use of the International System of Units (SI)". NIST Special Publication. 811: 45–69. doi:10.6028/nist.sp.811e2008. Retrieved 2019-11-07.
  3. ^ "NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically". NIST.gov. National Institute of Standards and Technology. 18 August 2025. Retrieved 2 November 2025.
  4. ^ Berger, Eric (2022-08-29). "Warning sign? NASA never finished a fueling test before today's SLS launch attempt". Ars Technica
  5. ^ Pauken, Michael (2011). Thermodynamics For Dummies. Indianapolis: Wiley Publishing Inc. p. 20. ISBN 978-1-118-00291-9.
  6. ^ Balmer, Robert (2011). Modern Engineering Thermodynamics. Oxford: Elsevier Inc. p. 10. ISBN 978-0-12-374996-3.
  7. ^ Grigull, Ulrich (1986). Heat Transfer. Retrieved 2022-08-29.
  8. ^ Magnum, B.W. (June 1995). "Reproducibility of the Temperature of the Ice Point in Routine Measurements". NIST Technical Note. 1411. Archived from the original on 2007-03-07. Retrieved 2007-02-11.