A degree is a unit of temperature, although the size of the unit varies depending on the particular temperature scale being used. The most common scales are those of Celsius (Centigrade), Kelvin and Fahrenheit. Calibrating each temperature scale requires defining two reference temperatures, with the difference between these divided into a certain number of degrees.

The Celsius scale is defined using the properties of water, specifically it’s melting and boiling points, which are assigned 0 ^oC and 100 ^oC, respectively. The scale between is divided into 100 degrees. The Fahrenheit scale uses the same reference temperatures, but defines them differently: 32 ^oF corresponds to the melting point of water, while 212 ^oF is taken to be the boiling point. The difference between these is divided into 180 degrees. The Kelvin scale uses degrees which are the same size as those of the Celsius scale, but it’s zero point is given by absolute zero, the temperature at which there is zero heat energy and thus it is an absolute scale. Temperatures in the Kelvin scale are written as, for example, 50 K, i.e. without the degree symbol.