Scales of temperature are a way to measure temperature quantitatively. A temperature scale is based on a single physical property of a simple thermodynamic system, called a thermometer that defines a scaling function mapping the temperature to the measurable thermometric parameter. Temperature scales that are based on measurements are called empirical temperature scales.
Empirical scales are most commonly a linear, functional relationship. All temperature scales use the International System of Units (S.I.), calibrated according to thermal properties of a particular substance or device. This is established by fixing two defined temperature points and defining temperature increments via a linear function of a response to the thermometric device. For example, the Celsius scale and the Fahrenheit scale were originally based on the linear expansion of a narrow mercury column within a limited range of temperature. Each of the scales however used different reference points and scale increments.
The most common scales used in thermodynamic calculations are Celsius, Fahrenheit, Rankine, and Kelvin.
0oC = 273.15 K = 32o F = 491.67o R