Sprinkler Run Time Calculator
How long to run your sprinklers, computed the way irrigation professionals do it: replace what evapotranspiration removed, corrected for your head type and how evenly the zone waters. Get your local ET from our evapotranspiration calculator, then dial in minutes per zone here.
How the math works
Run time isn’t a guess — it’s a water balance. Your landscape loses water at the reference ET rate, scaled by a crop coefficient (Kc) for what’s actually growing. Your sprinklers replace it at the zone’s precipitation rate, discounted by distribution uniformity because no zone waters perfectly evenly:
Divide by your watering days and you have minutes per zone per day. Every term is measurable: ETo from weather (calculate it here), precipitation rate from the head type or a catch-cup test, and DU from a catch-cup uniformity test.
Typical precipitation rates by head type
| Head type | Precipitation rate | Notes |
|---|---|---|
| Fixed spray | 1.3 – 1.7 in/hr | Fast — watch for runoff on slopes and clay |
| Impact | 0.8 – 1.2 in/hr | Older systems; uniformity varies widely |
| Rotor | 0.4 – 0.7 in/hr | Needs ~3× the minutes of spray zones |
| Rotary nozzle (MP-style) | 0.35 – 0.45 in/hr | Best uniformity of the bunch; long runs are normal |
| Dripline grid | 0.2 – 0.5 in/hr | For point-source drip use the drip run time calculator |
These are planning numbers. Actual rates depend on nozzle size, pressure, and spacing — a catch-cup test on the real zone beats any table.
The mistake that wastes the most water
Most controllers are programmed once, with the same minutes on every zone, tuned for July, and never touched again. That schedule is wrong eleven months of the year. ET in spring and fall is typically half of summer’s; running summer minutes year-round over-waters by 30–50%. If nothing else, change the seasonal adjust percentage monthly — or use a controller that reads ET itself.
Frequently asked questions
How long should I run my sprinklers?
Long enough to replace what the landscape lost to ET since the last watering — no more. For cool-season turf on spray heads at 5 mm/day ET watering 3 days a week, that’s roughly 20–30 minutes per watering day. The calculator above does this for your actual conditions.
Why do rotor zones need so much more time than spray zones?
Sprays apply about 1.5 in/hr; rotors about 0.5 in/hr. Same water requirement, one third the application rate, three times the run time. Copying one zone’s minutes onto every zone wastes water on some and starves others.
What is distribution uniformity and why does it change my run time?
DU measures how evenly a zone waters. At a typical 0.65, the driest spots get 65% of the average, so you run longer to keep them alive — that’s why run time is divided by DU. Improving DU with head adjustments or nozzle swaps is usually the cheapest water savings available.
Should I water every day for a few minutes?
Usually no. Short daily runs keep the top inch wet and train roots shallow. Fewer, deeper waterings — 2–3 days a week for turf in most climates — reach the full root zone. Exceptions: new seed, very sandy soil, heat waves.
Managing more than a backyard?
Droughtless computes this for every zone on a property, every day, from live weather — and watches for the failures a schedule can’t see: stuck valves, broken heads, dead zones.
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