Turn the 1-inch-per-week rule into real gallons and sprinkler minutes for your lawn size — deep and infrequent, the way turf actually wants it.
The 1-inch rule, made concrete
Established lawns want roughly an inch of water a week — rain included — delivered deep and infrequently rather than as a daily sprinkle. The conversion nobody does: one inch on one square foot is 0.623 gallons. Enter the lawn area, the weekly target, and (optionally) your sprinkler’s flow rate, and this calculator returns the gallons and the run time that actually delivers them.
How to use it
- Enter the lawn area in square feet.
- Keep 1 inch/week or adjust for climate and season.
- Add the sprinkler’s gallons-per-minute for the run-time answer — or measure it with the tuna-can test below.
The formula
A worked example
A 1,000 sq ft lawn needs 623 gallons a week — at a 2.5 GPM sprinkler, about 249 minutes, best split as two ~125-minute deep sessions rather than seven shallow ones. Deep watering pushes roots down; daily sprinkles keep them at the surface, which is why the daily-watered lawn is paradoxically the first to brown in a heatwave.