Cooling degree days are a type of degree days that are used to measure how much (in degrees), and for how long (in days), the outside air temperature was above a certain level. They are commonly used in calculations relating to the energy consumption required to cool buildings.

Cooling degree days can be considered as heating degree days in reverse: while heating degree days start adding up when the outside air temperature drops below the base temperature, cooling degree days start adding up when the outside air temperature rises above the base temperature. So the base temperature of cooling degree days is just the temperature above which the building needs cooling.