Plants and insects develop according to heat, not calendar days. Growing degree days add up the useful warmth each day above a base temperature, so you can predict flowering, harvest or pest emergence.
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Enter the day's high and low and the base for your crop. The calculator gives GDD per day, the total for a period and the days to reach your target.
simple: GDD = max(0, (high + low) ÷ 2 − base) modified: high and low are first limited to between base and upper threshold total = GDD per day × days
GDD in °F are 1.8 times GDD in °C; always compare targets in the same units.
With a high of 28 °C, a low of 14 °C and a base of 10 °C, each day gives 11 GDD, or 330 over 30 days. Corn needing 1,500 GDD would take about 137 such days. In °F, 82/57 °F with a 50 °F base gives 19.5 GDD a day.
A measure of heat accumulation: how many degrees each day's average is above a crop's base temperature, added up over time.
10 °C (50 °F) for corn and many warm-season crops; 0–5 °C (32–41 °F) for cool-season crops such as wheat and peas.
Typically 2,400–3,000 °F GDD (about 1,350–1,650 °C GDD) from planting to maturity, depending on hybrid.
It caps the high at an upper threshold (often 30 °C / 86 °F) and raises the low to the base before averaging.
GDD = (daily high + daily low) ÷ 2 − base temperature, with negative values counted as zero.
A growing degree unit: the same as a GDD, calculated with a 50 °F base and an 86 °F cap (the modified method).
Degree-days, in °C or °F. A value in °F is 1.8 times the same value in °C.