About the lawn watering calculator
Watering advice is usually given in inches per week, but sprinklers are set in minutes. The missing link is your sprinkler’s output rate, which you can measure in fifteen minutes with a few straight-sided cans.
Enter your lawn area, weekly target, any rain so far, and the measured rate. You’ll get total gallons and run time per watering day.
How to use this calculator
- Enter your lawn area.
- Enter your weekly water target (including rain).
- Subtract this week’s rainfall by entering it.
- Measure and enter your sprinkler output, then choose watering days per week.
Worked examples
- 5,000 sq ft, 1 in target, 0.25 in of rain
- 0.75 in needed → 5,000 × 0.75 × 0.623 = 2,338 gal
- Sprinkler output 0.5 in/hr → 90 minutes per week
About 2,338 gallons; two sessions of 45 minutes.
Measurement guidance
The catch-cup test
Place several straight-sided cans across the lawn, run the sprinkler for 15 minutes, measure the average depth, and multiply by four for inches per hour.
Uneven coverage
If cups vary a lot, adjust or move sprinklers before relying on the run time.
Frequently asked questions
How much water does a lawn need?
A commonly cited guideline is about an inch per week including rain, but grass type, soil, and climate change that. Local extension services publish regional advice.
Is it better to water deeply and less often?
Generally, yes. Deep, infrequent watering encourages deeper roots than frequent shallow watering.
When should I water?
Early morning reduces evaporation and helps the grass dry during the day.