Calculating Degree-Days

Climatologists use a variety of statistics to try to describe the climate of an area or site. One type of measure is degree-days.

Degree-days can be used to estimate the heating and cooling requirements of buildings. It is based on the idea that 18 °C is considered a comfortable temperature. When the temperature is above 18°C , cooling, either with a fan or air conditioning is desirable. When temperatures drop below 18°C, heating is required.

A degree-day is the number of degrees that the mean daily temperature is either above or below 18°C. So a summer day with a mean daily temperature of 23°C would account for 5 degree-days (23°C -18°C ) of cooling. A cold winter day with a mean daily temperature of -23°C would account for 41 degree-days of heating (the difference between -23°C and 18°C ).

Totaling the number of degree-days above 18°C for a year, this provides an estimate of annual cooling requirements. Summing the values below 18°C provides an estimate of heating needs. Heating demands in Saskatchewan are significantly higher than our cooling requirements.

With climate change, our cooling requirements are expected to increase, while our heating requirements should decrease. Individuals can access their SaskEnergy on-line accounts to obtain two-year monthly gas bill comparisons along with monthly average high and low temperatures. This illustrates how climatic data can help in determining the demand for natural gas.

Calculating Cooling Degree-Days - An Example:

For a hot summer month, if the average daily temperature is above 18°C for five days, you sum the total number of degrees above 18°C for those five days to get the number of degree-days of cooling in that month. Adding the values for each month gives you an annual total.

Measure Day 1 Day 2 Day 3 Day 4 Day 5 Total
Daily Minimum Temperature 15°C 17°C 19°C 16°C 17°C
Daily Maximum Temperature 32°C 32°C 35°C 30°C 26°C
Average Daily Temperature 23.5°C 24.5°C 27°C 23°C 21.5°C
Degree-Days above 18°C 5.5 6.5 8 5 3.5 28.5

Growing Degree Days is a similar measure used in agriculture as an index of crop growth. It is based on mean daily temperatures above 5°C .


  1. Barrow, E., 2009. Climate Scenarios for Saskatchewan PARC Publication (PP2009-01)
  2. Environment Canada,  National Climate Data and Information Archive: Glossary