Skip to main content
Calcimator

Irrigation Scheduling Calculator

Determine when and how much to irrigate based on evapotranspiration rate, current soil moisture, root depth, and soil water-holding capacity.

Inputs

in/day
% FC
in
in/ft
%
acres

Results

Days Until Irrigation

6.5 days

Water to Apply1.08 inches
Total Gallons Needed3,812,422 gal
Steady-State Interval10.8 days
Total Available Water in Root Zone5.4 in
How to Use This Calculator
  1. Enter the crop evapotranspiration (ET) rate in inches per day from local weather station or crop ET table data.
  2. Input current soil moisture as a percentage of field capacity, along with effective root depth and soil water-holding capacity.
  3. Set the management allowable depletion percentage and total field size in acres.
  4. Review the days until irrigation is needed and the recommended water application amount in inches.
  5. Use the total gallons needed and steady-state irrigation interval to program your pivot or drip irrigation controller schedule.

How the result changes with Current Soil Moisture

Current Soil MoistureDays Until Irrigation
10%0 days
35%0 days
65%3.2 days
90%8.6 days

What each input means

ET Rate
Crop evapotranspiration rate in inches per day. Check local weather stations or crop ET tables.
Current Soil Moisture
Current soil moisture as a percentage of field capacity. 100% = fully saturated root zone.
Effective Root Depth
Active rooting depth in inches. Corn: 36-48 in; soybean: 24-36 in; wheat: 36-48 in.
Soil Water Holding Capacity
Available water holding capacity in inches per foot of soil. Sandy: 0.8-1.2; loam: 1.5-2.0; clay: 1.8-2.5.
Management Allowable Depletion
Percentage of available water allowed to deplete before irrigating. 50% is standard for most crops.
Field Size
Total irrigated field area in acres.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    ET Rate = 0.25, Current Soil Moisture = 80, Effective Root Depth = 36, Soil Water Holding Capacity = 1.8 = 6 input(s) provided
  2. Calculate Days Until Irrigation
    Days Until Irrigation
    6.5 = 6.5
  3. Calculate Water to Apply
    Water to Apply
    1.08 = 1.08
  4. Calculate Total Gallons Needed
    Total Gallons Needed
    3812422 = 3812422

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Crop Farming

Fertilizer Application Rate

Calculate the pounds per acre of nitrogen, phosphorus, and potassium to apply based on soil test results and crop nutrient requirements.

Crop Farming

Crop Yield Estimator

Estimate expected crop yield in bushels per acre from plant population, ears or pods per plant, seeds per ear, and seed weight.

Irrigation

Crop Coefficient Calculator

Calculate growth-stage Kc values and crop ET using FAO-56 methodology for irrigation scheduling.

Hydrology

Evapotranspiration Calculator

Estimate reference evapotranspiration (ET₀) using a simplified Penman-Monteith approach from temperature, humidity, wind speed, and solar radiation.

Garden Planning

Garden Watering Calculator

Calculate weekly water needs for your garden based on size, temperature, rainfall, and soil type.

More in Agriculture & Farming.