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Growing Degree Days Calculator (GDD for Crops, Garden and Insects)

The growing degree days a day adds, how many days of that weather a crop stage needs, and the total after a run of such days.

Results

Growing degree days for the day 11.0 °C·d
Days to reach that stage at this pace 73 d
Accumulated over those days 330 °C·d
How it changes
Growing degree days for the dayHighest temperature of the day 5 – 40. Growing degree days for the day: 2 → 12Growing degree days for the day05101510203040Highest temperature of the day (°C)

The dashed line marks the value you entered.

What this tool does

Plants and insects develop with heat, not with the calendar. A growing degree day is the day's mean temperature above a base below which growth stops — commonly 10 °C (50 °F) for maize and many vegetables — with both the high and the low held to the base and to an upper cut-off (often 30 °C) so a hot afternoon or a cold night adds no more than it should. Seed packets and extension services give the GDD a variety needs to reach flowering or maturity; add up the daily values and you can forecast the stage far better than by counting weeks. Enter temperatures in °C (50 °F is 10 °C).

Formula

GDD = (T_max' + T_min') ÷ 2 − T_base, with both temperatures held between the base and the upper cut-off

Variables

SymbolMeaningUnit
txHighest temperature of the day°C
tnLowest temperature of the day°C
tbBase temperature of the crop°C
tcUpper cut-off temperature°C
tgGrowing degree days the stage needs°C·d
ndNumber of days like this—
GGrowing degree days for the day°C·d
DTDays to reach that stage at this paced
ACAccumulated over those days°C·d

Worked example

  • Highest temperature of the day28 °C
  • Lowest temperature of the day14 °C
  • Base temperature of the crop10 °C
  • Upper cut-off temperature30 °C
  • Growing degree days the stage needs800 °C·d
  • Number of days like this30
  • Growing degree days for the day11.0 °C·d
  • Days to reach that stage at this pace73 d
  • Accumulated over those days330 °C·d

Limitations

  • The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
  • The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.