The Rankine scale is a thermodynamic (absolute) temperature scale. It is based around absolute zero. Rankine is similar to the Kelvin scale in that it starts at absolute zero and 0°Ra is the same as 0K but is different as a change of 1°Ra is the same as a change of 1°F (Fahrenheit) and not 1°C (Celsius). Note that the abbreviation °R is ambiguous, as it can also refer to the Réaumur scale.
The Kelvin and Rankine temperature scales are defined so that absolute zero is 0 kelvins (K) or 0 degrees Rankine (°R). The Celsius and Fahrenheit scales are defined so that absolute zero is −273.15 °C or −459.67 °F.
The Rankine scale was originally used in the United States.