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GDU Calculator — Growing Degree Units

Calculate daily corn growing degree units with the 86/50 °F method.

Your inputs

Change any value — everything updates instantly.

Highest temperature of the day.

Lowest temperature of the day.

Try an example

Growing degree units

22.5 GDU

This means corn gained 22.5 heat units today towards its next growth stage.

40°50°60°70°80°86°100°low 60high 8522.5 of 36 possible GDU today
Corn growth range 50–86 °FYour temperaturesHeat units
22.5 GDU

What you are seeing

The bar is a thermometer from 40 to 100 °F; the green band is 50–86 °F, where corn grows.

Your high of 85 °F is used as 85 °F and low of 60 °F as 60 °F.

The average above 50 °F gives 22.5 GDU.

High used

85 °F

Capped at 86 °F — hotter adds no growth.

Low used

60 °F

Raised to 50 °F — corn doesn't grow below.

Days to 100 GDU

4.4 days

At this pace, days to gain 100 GDU.

Result explanation: Today's heat for corn

22.5 GDU today.

Real-life comparison: Corn needs roughly 100–150 GDU to emerge; the maximum possible in one day is 36.

Low, normal or high? Moderate growth.

Graph and details

6073859811001223Daily high (°F)GDU

GDU against daily high

How to read this chart: GDU flattens above 86 °F because extra heat doesn't speed corn up. The red dot is today.

What this calculator does

Calculates corn growing degree units using the standard 86/50 °F method.

What your result means

22.5 GDU.

Add daily values to track total season heat.

Seed companies list GDU needed for each hybrid.

The formulas

Clip both temperatures to 50–86 °F, average them, subtract the 50 °F base.

1. Modified growing degree units (86/50)

GDU = (min(Tmax, 86) + max(Tmin, 50)) ÷ 2 − 50

Symbols

Tmax
Daily high (°F)
Tmin
Daily low (°F)

Why this formula works

Corn develops little below 50 °F and no faster above 86 °F.

Unit check

°F − °F = degree units ✓

Worked example

  1. High 85, low 60
  2. (85 + 60) ÷ 2 = 72.5
  3. 72.5 − 50 = 22.5 GDU

Common mistakes

  • Not capping the high at 86 °F.
  • Using Celsius values in the °F formula.

Working for your numbers

  1. High used = min(85, 86) = 85
  2. Low used = max(60, 50) = 60
  3. (85 + 60) ÷ 2 − 50 = 22.5 GDU

Today added 22.5 GDU.

Frequently asked questions

GDU vs GDD?

Same idea. GDU is the term commonly used for corn.

Other crops?

Many use different base temperatures; this page uses corn's 50/86 °F.

Using Celsius?

Convert to °F first, or use the Celsius version with 10/30 °C limits.

Where do I get temperatures?

Your local weather station's daily high and low.

Symbols and assumptions

GDU
Growing degree units ()
  • 86/50 °F corn method.
  • Temperatures in °F.

Sources and review

Reviewed 2026-09-25 · Next review 2027-09-25

Corn growth and development — GDUPurdue University Agronomy (Nielsen)

Important limitation. Educational estimate. Field conditions also affect growth.

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