Cooling Degree-Day (CDD) is a measure of the need for air conditioning based upon outdoor temperatures. Cooling degree-days are calculated as follows:
Daily mean temperature - 18.3°C
(65°F)
For example, if the average temperature for a given day was 85 °F, then that would be a 20 degree day. Cooling degree days can be added over periods of time to provide a rough estimate of seasonal cooling requirements. For example, the number of cooling degree-days in Florida is likely to be much higher than those in Alaska.
See also Heating Degree-Day (HDD).