Celsius, historically known as centigrade, is a scale and unit of measurement for temperature.The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval.

Fahrenheit (symbol °F) is a temperature scale based on one proposed in 1724 by the German physicist Daniel Gabriel Fahrenheit (1686–1736), after whom the scale is named.

The kelvin is a unit of measure for temperature based upon an absolute scale. It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F). In other words, it is defined such that the triple point of water is exactly 273.16 K.

Rankine is a thermodynamic temperature based on an absolute scale named after the Glasgow University engineer and physicist William John Macquorn Rankine, who proposed it in 1859. The symbol for degrees Rankine is °R

[°C] = ([°F] − 32) × 5/9

[K] = ([°F] + 459.67) × 5/9

[°R] = [°F] + 459.67