About the Sprinkler Run Time Calculator
This sprinkler run time calculator tells you how many minutes to run an irrigation zone to put down a target depth of water. Most lawns need roughly 1 to 1.5 inches per week in summer, but a spray-head zone and a rotor zone apply water at very different speeds, so the right run time depends on your system’s precipitation rate.
You can enter the precipitation rate directly (from the nozzle chart), calculate it from the zone’s flow in gallons per minute and the area it covers, or measure it with a catch-cup test — set out straight-sided cans, run the zone for a timed period and average the depth collected. Add your weekly target, how many days per week you water and an efficiency factor to cover uneven coverage, and the tool returns minutes per watering, minutes per week and the gallons used.
If water starts running off before the cycle ends, split the run time into two or three shorter cycles with a 30–60 minute soak in between. Adjust the weekly target for rainfall, season and local watering restrictions.
With the default inputs, the run time per watering is 17 min. Change any value above to recalculate instantly.
How to use the sprinkler run time calculator
- 1Choose how you know the zone’s precipitation rate: nozzle chart, flow and area, or a catch-cup test.
- 2Enter the rate, or the flow and area, or the cup depth and test time.
- 3Set how many inches per week the lawn or bed needs.
- 4Choose how many days per week you water.
- 5Set an efficiency factor, then program the minutes per watering into your controller.
Formula and method
The precipitation rate (PR) is how many inches of water a zone applies per hour. From flow, PR = 96.25 × GPM ÷ area in square feet, where 96.25 converts gallons per minute over square feet into inches per hour (60 min × 231 cu in per gallon ÷ 144 sq in per sq ft). From a catch-cup test, PR is the average depth collected divided by the test time in hours.
The weekly target is divided by the system efficiency to get the gross depth to apply (a less uniform system has to run longer so the dry spots still get enough), then split evenly across your watering days. Dividing the depth per watering by the precipitation rate gives hours, times 60 for minutes. Water used is depth × area × 0.623 gallons per square foot-inch.
- PR
- Precipitation rate, inches per hour
- GPM
- Total flow of all heads in the zone, gallons per minute
- Area
- Area the zone waters, square feet
- Efficiency
- Fraction of applied water that usefully reaches the root zone
Worked examples
Spray-head zone at 1.5 in/hr, 1 inch a week over 3 days
At 80% efficiency you need to apply 1 ÷ 0.8 = 1.25 inches a week, or about 0.42 inches per watering. At 1.5 in/hr that takes 0.4167 ÷ 1.5 × 60 ≈ 17 minutes, three times a week. Over 1,000 sq ft that is about 779 gallons a week.
Rotor zone: 12 GPM over 2,000 sq ft, 1.25 in over 2 days
The precipitation rate is 96.25 × 12 ÷ 2,000 = 0.58 in/hr. At 75% efficiency the zone must apply 1.67 inches a week, 0.83 inches per watering, which takes about 87 minutes each time. Total use is about 2,078 gallons a week.
Catch-cup test: 0.3 inches in 15 minutes
Collecting 0.3 inches in a quarter hour means the zone applies 1.2 in/hr. Splitting 1 inch over two days is 0.5 inches per watering, which takes 0.5 ÷ 1.2 × 60 = 25 minutes.
Frequently asked questions
How long should I run my sprinklers?+
Spray-head zones usually need 10–20 minutes per cycle and rotor zones 30–60 minutes to apply about half an inch, but the only reliable answer comes from your own precipitation rate. Measure it with a catch-cup test and use this calculator.
How much water does a lawn need per week?+
Most cool- and warm-season lawns need about 1 to 1.5 inches per week during active summer growth, including rainfall, and less in spring and fall. Sandy soils may need it split into more frequent applications.
How do I do a catch-cup test?+
Place 6–12 identical straight-sided cans or cups across the zone, run it for 10–20 minutes, then measure the water depth in each. Average the depths and divide by the run time in hours to get inches per hour.
Why do spray heads and rotors need different run times?+
Fixed spray heads put out water quickly over a small area, typically 1.5–2 inches per hour, while rotors throw streams over a larger area at roughly 0.4–0.8 inches per hour. Rotor zones therefore need about three times longer to apply the same depth.
What is cycle and soak?+
Cycle and soak splits one long run into several shorter ones separated by a pause, so water has time to soak in. It prevents runoff on clay soils and slopes when the precipitation rate is higher than the soil can absorb.