Cooling Degree Days (CDD) Calculator
Calculate cooling degree days to estimate air conditioning energy demand.
Plan HVAC costs and compare cooling needs across different climates.
What Are Cooling Degree Days? Cooling Degree Days (CDD) measure how much and for how long the outside air temperature rises above a baseline (typically 65 degrees F or 18 degrees C). Each degree above the baseline for one day equals one CDD. The higher the CDD total, the more energy needed for cooling (air conditioning).
The Formula Daily CDD = max(0, Average Daily Temperature - Base Temperature). If the average temperature is 85 degrees F and the base is 65 degrees F: CDD = 85 - 65 = 20 degree days. If the average temperature is below 65 degrees F, the CDD for that day is zero.
CDD vs HDD HDD measures heating demand (cold weather). CDD measures cooling demand (hot weather). Together they describe a location’s total climate-control energy needs. A city like San Diego has low values for both (mild year-round). Phoenix has very high CDD but low HDD. Minneapolis has very high HDD but moderate CDD.
Typical Annual CDD Values (US) Phoenix: ~4,000 CDD. Houston: ~2,800. Miami: ~4,300. Atlanta: ~1,800. New York: ~1,100. Chicago: ~800. Seattle: ~200. These values help building designers specify appropriate cooling equipment sizes.
Energy Cost Estimation Similar to HDD, a building’s cooling energy correlates with its CDD total. If a building uses 500 kWh of electricity for cooling in a month with 400 CDD, the cooling coefficient is about 1.25 kWh per CDD. This lets you forecast summer electricity costs from weather data. Air conditioning efficiency (SEER rating) significantly affects the actual energy consumed per CDD.