Growing Degree Days
Accumulated growing degree days from a daily Tmax/Tmin series, a crop base temperature, and an optional upper cutoff.
Example
You enter
- Daily Tmax/Tmin pairs (e.g. 92/64, 90/62) tmax 92, tmin 64
- Base temperature (°F) 50
- Upper cutoff (F, 0 = none) 86
- Method modified
You get
- Accumulated GDD 25
- Days counted 1
Checked against published worked examples from: USDA / NWS GDD method + McMaster & Wilhelm 1997.
Details, formula, and sources
Scopeby the standard or modified method.
Formula or tableGDD = ((min(Tmax,cutoff) + Tmin_adj)/2) - base, floored at 0. The modified method caps Tmax at the cutoff and floors Tmin at the base before averaging.
Source and editionPer the USDA / NWS growing-degree-day method and McMaster & Wilhelm (1997), 'Growing degree-days: one equation, two interpretations,' Agric. & Forest Meteorology 87, by name.
Free accessFree at university extension sites and agresearch indexes; corn 50/86 F is the land-grant convention.
What governsEstimate. AHJ and licensed professional govern.
API field namesdays_series, base_f, cutoff_f, method, accumulated_gdd, days
- Base/cutoff crop-specific (corn 50/86 F); user-suppliedland-grant extension