Degree Days are a way to help determine how much warmth or cold there has been, typically over a season such as winter, summer or a plant’s growing season. Degree Days are used to determine a building’s typical heating or cooling requirements over a season. They are used in agriculture, farming and gardening to plan plant and crop planting, management and harvest dates. In this blog we provide Microsoft Excel-based degree day calculator that you can download and use.
To download the interactive Microsoft Excel Degree Days Calculator, please download the file
To start using the Degree Day Workbook, sign up for a Weather Data Services Product Key. After sign up, you can find your product key under your account details.
Paste your product key into the Growing Degree Calculator Introduction worksheet. Then enter an address for the location to look up Degree Days. The location address can be a full address, a partial address (such as “city, country” ) or latitude, longitude value (40.2,-75.3).
Once the data is refreshed, the Heating Degree Days, Cooling Degree Days and Growing Degree Days will be presented in three separate worksheets. You can click between them and modify the degree day parameters on each of them.
Using Weather Data to Calculate Degree Days
Last year, I wrote a article Create a Growing Degree Days Calculator in Microsoft Excel. This new calculator expands on that work to include degree day calculators for Heating Degree Days and Cooling Degree days. In addition, the updated calculator makes it easy to get started by removing the need to install an Excel add-in. In this new version, we use the Weather API to load weather history data and weather forecast data using Excel Web Queries.
There are three degree calculators included in this workbook.
Heating Degree Days
Heating Degree Days (HDD) measure the number of effective day when the average daily temperature fell below 65F. At 65F, buildings are expected to turn on their heating when the temperature drops below this point. If the average daily temperature is colder, say 32F, then the building will require more heating. Therefore for for every degree lower than 65, an extra degree is added. A day that has a mean temperature of 60F will have a HDD value of five. A day that has a mean temperature of 32F will have a HDD value of 33.
The heating degree days can be added up over a season to show the total amount of HDD for that particular season.
Cooling Degree Days
Cooling Degree Days (CDD) give an indication of how hot a summer is by creating a picture of the amount of cooling required. CDD are calculated in a similar way to heating degree days however they measure the degree days above 65F. For example, a day where the average temperature is 75F will have a cooling degree value of 10F.
Growing Degree Days
Growing Degree Days (GDD) give a way to manage the planting, management and harvest of a crop on the farm or garden. They use the idea that many species of plants grow and flourish above a minimum temperature. The warmer it is above that temperature then the faster the plant will mature. This is considered a more accurate way to estimate the growth stage of a plant compared to the age of a plant. This approach considers that, assuming other factors such as irrigation are equal, a plant will grow faster if it is warmer. However, at some higher temperature, the plant may not grow faster if it gets warmer.
If we consider corn, we can say that corn does not grow unless the temperature is at least 50F. Corn will mature faster if the temperature is warmer until 86F when corn reaches its maximum maturation rate. We use 50 as the minimum temperature in the same was a 65F was the minimum for Cooling Degree Days. So if a day has an average temperature of 65, that day will have 15 Growing Degree Days for corn.
Different crops have different values for the minimum temperature (Tbase) and the maximum temperature (Tmax). Cumulative growing degree days across the growing season can be used to indicate when the crop requires fertilizer or may be ready for harvesting. For example some varieties will reach maturity in around 2000-2500 GDD.
Details of the Growing Degree Day Calculation
The full Growing Degree calculation and Microsoft Excel implementation can be found in last year’s article. If you are interested in additional weather data for calculating degree days or any other weather climate analysis, check out our Weather Data platform that provides weather history data, 15-day weather forecast data and climate summaries.