Irrigation Schedule Calculator

Work out irrigation schedule instantly with clear inputs, formula shown and shareable results.

About Irrigation Schedule Calculator

Crop water use is ETc = Kc x ETo. Dividing the readily available water held in the root zone by ETc gives the number of days before the crop reaches its allowable depletion, which is the irrigation interval. The depth applied must be grossed up by the application efficiency because part of every irrigation is lost to runoff, wind drift and deep percolation.

Formulas

Crop water use

ETc = Kc x ETo

Interval and depth

Interval (days) = readily available water / ETc; gross depth = net depth / efficiency

Worked example

With the default values below, Irrigation Schedule Calculator returns Irrigation Interval of 6.35. Change any input above and every figure here is recalculated in your browser.

Inputs used

Reference Evapotranspiration (ETo)minimum 0.1 mm/day: 6 mm/day
Crop Coefficient (Kc)accepts 0.1–1.5: 1.05
Readily Available Soil Waterminimum 1 mm: 40 mm
Application Efficiencyaccepts 10–100 %: 75 %

Results

Irrigation Interval: 6.35
Crop Water Use (ETc): 6.30
Gross Application Depth: 53.33
Weekly Net Requirement: 44.10

Step by step

1Values used
2Crop water use
3Interval and depth
4Irrigation Interval= 6.35
5Crop Water Use (ETc)= 6.30
6Gross Application Depth= 53.33
7Weekly Net Requirement= 44.10

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Where do I get ETo and Kc?

ETo comes from a nearby weather station or the FAO Penman-Monteith estimate. Kc depends on crop and growth stage — roughly 0.3-0.5 at emergence, 1.0-1.2 at mid-season and 0.6-0.9 at maturity.

What efficiency should I assume?

Surface and furrow systems are typically 50-65%, sprinklers 70-80% and well-managed drip 85-95%. Lower efficiency means more water must be pumped for the same crop benefit.