Rankine is a thermodynamic temperature scale named after the Scottish engineer and physicist William John Macquorn Rankine, who proposed it in 1859.

The symbol is R (or Ra if necessary to distinguish it from the Rømer and Réaumur scales). Occasionally this is written °R, but as with the Kelvin scale the usage of the degree symbol is incorrect. Zero on both the Kelvin and Rankine scales is absolute zero, but the Rankine degree is defined as equal to one degree Fahrenheit, rather than the one degree Celsius used by the Kelvin scale. A temperature of −459.67 °F is exactly equal to 0 R.

Many engineering fields in the U.S. measure thermodynamic temperature using the Rankine scale. However, throughout the scientific world where measurements are made in SI units, thermodynamic temperature is measured in Kelvin.

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

	Kelvin	Celsius	Fahrenheit	Rankine
Absolute zero (by definition)	0 K	−273.15 °C	−459.67 °F	0 R
Freezing point of water	273.15 K	0 °C	32 °F	491.67 R
Triple point of water (by definition)	273.16 K	0.01 °C	32.018 °F	491.688 R
Boiling point of water	373.1339 K	99.9839 °C	211.9710 °F	671.641 R

References

1. http://www.physorg.com/tags/temperature/
2. The ice point of purified water has been measured to be 0.000089(10) degrees Celsius - see
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.

See also

• Comparison of temperature scales