Calculating degree days is important in calculating certain home or commercial heating or cooling requirements or calculating proper agricultural planting requirements. Regardless of the purpose of the calculation, the process for calculating degree days is the same. The general formula for calculating degree days is: Degree Days = Average daily temperature - Base temperature = (maximum + minimum) / 2 - Base temperature. For this example, assume a base of 10 degrees C with a minimum temperature of 7.22 degrees C and a maximum temperature of 21.1 degrees C.
Decide on the degree day base to use. This number will differ depending on, for example, the type of crop to be planted or the type of crop pest to be eradicated. For our example, we will use the arbitrary number of 50.
Calculate the average temperature by adding the maximum and minimum temperatures, then dividing by two. In this case, Average = 70 + 45 / 2, so Average = 57.7.
Calculate the degree days by subtracting the base from the average. Degree Days = 57.7 - 50. So, degree days = 7.7.
Use the degree days calculation to establish if the time is right for crop planting or pest eradication.
The degree day base you use will depend on what you want to establish. For example, the degree day base for one crop might be lower than for a crop that should be planted later in the season.