Rankine Conversion (ºR)

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Wordwide use:

Rankine is an absolute temperature measurement used mainly in the United States.

In engineering Rankine is often used in the design of power plants, refrigeration systems and industrial processes. It is particularly useful as it directly relates temperature to energy making calculations more straightforward.

Most countries use Celsius or Kelvin as their primary temperature scales (Celsius for common use and Kelvin as the absolute scale).


Rankine is an absolute temperature scale based on Fahrenheit with the degree intervals being the same. The difference is that Rankine starts at absolute zero; the point at which all molecular motion ceases.

The Rankine scale is often interchangable with the Kelvin scale which is the primary unit of temperature in the International System of Units (SI). Rankine is easily converted to Fahrenheit by simply adding 459.67. This means that the size of one degree Rankine is equal to the size of one degree Fahrenheit.


The Rankine scale was named after the Scottish engineer and physicist William John Macquorn Rankine who was born in 1820. He made significant contributions to the field of thermodynamics and is best known for his work on heat engines.

Common references:

Absolute Zero, 0ºR

Melting point of ice, 491.67ºR

Warm summer's day in a temperate climate, 531ºR

Normal human body temperature, 558.27ºR

Boiling point of water at 1 atmosphere, 671.67ºR

Usage context:

The Rankine scale is used in thermodynamics particularly in heat engines and power cycles. Rankine is akin to Fahrenheit as Kelvin is to Celsius.

The scale is also occasionally used in some specialized fields such as aerospace engineering and materials science however the Rankine scale is not normally used in everyday life or in most scientific disciplines.

What happens at absolute zero (0K)?:

At absolute zero, 0 Kelvin (0K) or -273.15 degrees Celsius, the temperature is at the lowest possible point anything can possibly be. At this temperature the kinetic energy of atoms and molecules is zero causing them to come to a complete standstill. All molecular motion ceases and matter becomes still.

Several amazing phenomena occur here. As there is no molecular motion there is no heat energy and this has significant implications for the physical properties of the substance. For example, materials become very brittle and their electrical resistance becomes zero. Gases and liquids freeze into solids.

Scientists have never cooled anything down to absolute zero. However they have been able to see the effects of approaching absolute zero. This has provided insights into the behavior of matter and have led to the understanding of superconductors and Bose-Einstein condensates.

Why can't you go below 0ºR?:

Rankine is an absolute measurement of temperature meaning it starts at absolute zero, the lowest possible temperature in our universe. Absolute zero is 0 Rankine(K) or -459.67 degrees Fahrenheit(°F). The Rankine is based on the average kinetic energy of particles in a substance.

You cannot have a negative Rankine value because at 0K there is no kinetic energy in the particles and are at their lowest possible state of motion. It is impossible for a system to have less energy than zero.

Negative Rankine would imply that a system has a negative thermal energy which breaks the principles of thermodynamics. It is important to remember that negative temperatures exist in other temperature scales such as the Celsius and Fahrenheit.


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