How this calculation works
One millimetre over one square metre is one litre. Divide the net target by entered efficiency, then divide gross litres by total simultaneous emitter flow.
Runtime hours = area m² × net depth mm / (efficiency × emitter count × L/hour per emitter)A worked example
A 100 m² zone with a 4 mm net target needs 400 L net or 500 L gross at 80% efficiency. One hundred 2 L/hour emitters need 2.5 hours, or two 75-minute cycles.
Good to know
Entered target and efficiency are not crop-water advice. Equal constant emitter flow assumed. No pressure, clogging, rain, soil infiltration, soak gaps or pump duty calculation.
Reference: University of Minnesota Extension: irrigation uniformity concepts (opens in a new tab) ↗
Translate depth into a water volume
Depth is useful because it expresses water relative to area. A 4 mm target over 100 m² becomes 400 L without needing a separate conversion constant when these units are used.
The target is not supplied by the calculator. It represents the scenario you want to test, and it does not establish crop demand, soil storage or an appropriate watering schedule.
The farm machine field capacity and cost calculator adds estimate field capacity after explicit overlap and delays, then calculate clock hours, fuel and operating cost without counting efficiency losses twice.
Net target and gross delivery differ
An entered 80% efficiency means only 80% of gross delivered water is counted toward the stated net target. Dividing by 0.8 supplies the gross amount rather than adding only 20% to the net amount.
Total flow assumes every entered emitter operates at the same time and at the same measured output. Nominal label flow can differ from actual field delivery under pressure variation or blockage.
Cycle length does not include soak time
Equal cycles divide active runtime only. If you require pauses between them, those pauses must fit into the real schedule separately. The operating-window result compares active time, not an automatic irrigation program.
The catch-can tool linked below measures a different issue: observed spatial delivery. A single efficiency input should not be treated as evidence that every location receives the same depth.
Use the result with the next measurement
The irrigation catch can uniformity calculator measures spatial delivery using observed catches. This runtime tool assumes equal emitter outputs, so it cannot use a single runtime to prove that every location receives the target depth.
Entered target and efficiency are not crop-water advice. Equal constant emitter flow assumed. No pressure, clogging, rain, soil infiltration, soak gaps or pump duty calculation.
A few questions, answered
Does the tool recommend a water depth?
No, the depth is your input scenario.
Are cycle pauses included?
No, output is active run time only.
Does emitter count mean all installed emitters?
Enter those running simultaneously in this zone.