Understanding Degree Days: Energy Demand and Climate

2026-04-25

Degree days are a specialized but incredibly useful climate metric. A heating degree day (HDD) measures how much and for how long the temperature falls below a base point, typically 18C. A cooling degree day (CDD) does the same for temperatures above that point. If the average temperature on a given day is 10C, that is 8 HDD

. If it is 25C, that is 7 CDD. Summing these over a month or year gives a powerful indicator of energy demand for heating and cooling buildings. Cities like Reykjavik accumulate over 5,000 HDD per year, meaning enormous heating energy demand. Dubai, conversely, racks up over 3,000 CDD, reflecting massive air conditioning needs

. Energy companies use degree days to forecast demand, plan capacity, and benchmark building energy efficiency. Our Degree Days Calculator tool lets you compute these values for any of our 50 tracked cities..