Irrigation Run Time Calculator

A zone's precipitation rate is how fast it wets the ground, as a depth per hour. From the design it is the total flow of all heads or emitters spread over the zone area: in metric, litres per minute × 60 over square metres gives millimetres per hour directly (a litre on a square metre is a millimetre); in US units, gallons per minute × 96.25 over square feet gives inches per hour, where 96.25 is exactly 60 × 231 ÷ 144. From the ground it is a catch-cup test: the average depth collected in a timed run, scaled to an hour. Measured rates include the real overlap and pressure; design rates do not.

Run time is the depth you want divided by the rate. Because not all of it reaches the root zone evenly — wind drift, evaporation, dry spots and overlap — the depth is first divided by an application efficiency (or distribution uniformity) so the driest part gets enough. That figure comes from an audit of your system or the design assumption you use; 100 % is flagged as the ideal. Cycle-and-soak simply splits the same minutes into shorter runs for soils or slopes that cannot take water quickly; the soak pause is yours to choose.

How much water a lawn, bed or crop needs per week depends on the plant, the season, the soil, the climate and local restrictions; that is an agronomic or regulatory question. Enter the weekly or per-event depth from your own source (evapotranspiration data, the nursery, the water authority) and, optionally, the days per week, and the page divides it into run times. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.