Free Irrigation Water Requirement calculator with clear step-by-step results.
Converts an agronomic water depth into controller runtimes. Net demand is grossed up for distribution uniformity - no sprinkler system waters evenly, so you must over-apply to give the driest area enough - then divided by system flow and split across the cycles you schedule.
Gross water required
Litres = area m2 x depth mm / distribution uniformity
Runtime per cycle
Minutes = gross litres / flow rate / cycles per week
Above 80% for a well-designed drip system, 70-75% for good rotor sprinklers and often under 60% for mismatched spray heads. Improving uniformity saves more water than reducing runtime.
If it exceeds the soil's infiltration rate, water runs off instead of soaking in. Heavy clay may accept only 5-8 mm per hour, which forces short, repeated cycles.