The GDU (Growing Degree Units) Calculator helps farmers, agronomists, and agricultural planners determine the heat accumulation needed for crops to grow. GDU is an important measurement in agriculture because it predicts how fast a crop will develop. Different crops need different amounts of heat to reach each growth stage, and by calculating GDUs, growers can better plan planting, irrigation, fertilization, and harvest schedules.
This tool calculates GDUs based on daily temperature inputs, especially for heat-sensitive crops like corn, soybeans, and wheat. Since plant development is closely linked with temperature, GDUs offer a way to estimate crop maturity regardless of the calendar date. This makes the calculator valuable for managing seasonal timing and improving yields.
This calculator falls under the agriculture and crop growth calculators category.
formula
GDU Formula:
GDU = (Daily Maximum Temperature + Daily Minimum Temperature) ÷ 2 − Base Temperature
Variables Explanation:
Daily Maximum Temperature is the highest temperature recorded during the day.
Daily Minimum Temperature is the lowest temperature recorded during the day.
Base Temperature is the threshold temperature below which crop growth does not occur (commonly 50°F for corn).
Important Rules and Adjustments:
If Daily Maximum Temperature > 86°F, then use 86°F instead.
If Daily Minimum Temperature < 50°F, then use 50°F instead.
If the result of the GDU formula is less than 0, set GDU = 0 (no negative values).
Adjusted Formula (for crops like corn using standard limits):
GDU = [(min(Daily Max, 86) + max(Daily Min, 50)) ÷ 2] − 50
This version ensures the temperatures are capped and floored appropriately.
GDU Quick Reference Table
The following table helps users get an approximate GDU value quickly based on daily temperatures. This is especially helpful for farmers tracking weather manually.
| Daily Max Temp (°F) | Daily Min Temp (°F) | Adjusted GDU |
|---|---|---|
| 90 | 45 | 18 |
| 86 | 50 | 18 |
| 84 | 52 | 18 |
| 80 | 60 | 20 |
| 78 | 55 | 16.5 |
| 76 | 50 | 13 |
| 72 | 50 | 11 |
| 68 | 50 | 9 |
| 65 | 50 | 7.5 |
| 60 | 50 | 5 |
Note: All values are calculated using the adjusted formula with a base temperature of 50°F and standard max/min caps.
Example
Suppose the Daily Maximum Temperature is 90°F, and the Daily Minimum Temperature is 45°F. Let’s calculate the GDU:
First, apply the caps:
Adjusted Max = min(90, 86) = 86
Adjusted Min = max(45, 50) = 50
GDU = [(86 + 50) ÷ 2] − 50
GDU = (136 ÷ 2) − 50
GDU = 68 − 50
GDU = 18
So, the GDU for the day is 18.
Most Common FAQs
Corn typically requires between 2,400 and 3,000 GDUs from planting to maturity, depending on the hybrid and region. Daily values around 15–20 are common during the growing season.
If the daily max exceeds 86°F, it’s capped at 86 because corn doesn’t grow faster above that point. If the daily min drops below 50°F, it’s set to 50 because growth stops below that temperature. This makes sure the GDU reflects only useful heat.
Yes, but the base temperature and max/min limits may vary by crop. For example, cool-season crops like wheat or lettuce may have a different base temperature, such as 40°F. Always check the crop-specific requirements.