Free calculator
How long should you water?
A weekly target is only useful if you know your sprinkler's output. Measure it, subtract effective rain, and run the math.
Watering runtime
Weekly runtime
120minutes
Per session
60minutes
Water needed
3,115gal
Per session
1,558gal
Rain credited
0in
The formula
Weekly runtime = (target inches − effective rain) ÷ application rate in inches per hour × 60. Gallons = inches applied × area × 0.623. The calculator credits 80% of recent rain, which is a rough allowance for runoff and evaporation.
Measure your sprinkler
Scatter straight-sided cups across the lawn, run the sprinkler for 15 minutes, and measure the average depth. Multiply by four to get inches per hour. One cup in one spot is not a measurement.
Water deeply, less often
Most lawns do better with one or two deep sessions than with a short daily run. If water starts running off, split the session into two cycles with a short pause. Adjust for slope, soil type, and heat; the calculator cannot see your lawn.
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