Heating & Cooling Degree Days Calculator

The 65 degree base is a convention, and a well-insulated building may have a lower balance point. Solar gain, wind, humidity and occupancy affect real demand. A single day's value says little, and totals across a season are more meaningful.

Days with high and low averaging the same can have different needs.

Heating & Cooling Degree Days: formula

NOAA convention: heating degree days = max(0, 65°F − avg temp); cooling degree days = max(0, avg temp − 65°F)

National Weather Service: Heat Index and Wind Chill · EIA: Degree-day definitions

Heating degree days from average daily temperature (°f)

Average daily temperature (°F)	55
Heating degree days	10
Cooling degree days	0

Enter a daily average temperature in °F. The high-plus-low divided by two is one conventional daily approximation; other hourly or station averaging methods can differ. This tool uses a 65°F reference for both heating and cooling degree days.

That is a weather-index convention, not a measured balance point for every building.

Heating & Cooling Degree Days: changing Average daily temperature (°F)

Heating degree days: assumed Average daily temperature (°F) scenarios.
Average daily temperature (°F)	Heating degree days	Cooling degree days
44	21	0
50	15	0
55 (example)	10	0
61	4	0
66	0	1

Heating & Cooling Degree Days: compare input ranges

Heating & Cooling Degree Days Calculator: Heating degree days with each input moved on its own, every other input held at the worked-example value.
Input	Tested from	To	Heating degree days: low input	Heating degree days: high input	Swing
Average daily temperature (°F)	50	61	15	4	11 (110%)

Heating & Cooling Degree Days: individual input comparisons

Heating & Cooling Degree Days Calculator: change one input at a time; other values remain at the stated example.
Input	Value	Heating degree days	Cooling degree days
Average daily temperature (°F)	44	21	0
	50	15	0
	55	10	0
	61	4	0
	66	0	1

Heating & Cooling Degree Days: values and definitions

Worked-example inputs and the results they produce for the Heating & Cooling Degree Days Calculator.
Quantity and definition	Value used
Average daily temperature (°F)	55
Heating degree days	10
Cooling degree days	0

Average daily temperature (°F): half and double

Heating & Cooling Degree Days scale comparison; assumed inputs.
Average daily temperature (°F)	Heating degree days
27.5	37.5
55	10
110	0

Common error: Treating a degree-day figure as a direct dollar prediction for a utility bill. It's a weather-demand proxy, and the actual cost still depends heavily on a building's own insulation, equipment efficiency and utility rate structure.

Degree days translate a single average temperature into a rough proxy for heating or cooling demand relative to a 65°F baseline, a threshold chosen because it approximates the temperature below which most buildings historically needed heat and above which they needed cooling: useful for comparing relative demand across days, not for predicting an actual utility bill.

Use degree days to compare relative demand between days or track a seasonal trend, not as a direct stand-in for actual energy cost, which also depends on a building's insulation, rates and equipment efficiency.

See temperatures on the temperature converter, cold and heat feels on the wind chill and heat index pages, and energy on the energy converter. The energy and utilities categories cover bills and heating costs, and the dew point page covers humidity.

Does higher fuel per degree day prove equipment deterioration?

No. Occupancy, hot-water load, billing dates, thermostat settings and other nonweather uses can change that ratio.

Can I use a monthly mean instead of daily values?

That can lose information because the positive heating/cooling differences are clipped each day. Sum the daily values for the intended period.

Heating & Cooling Degree Days Calculator