Lawn Watering Calculator
Convert inches of water into gallons for your lawn, and estimate how long to run a hose or sprinkler at a given flow rate.
How it works
Gallons = area(ft²) × depth(in) × 0.6234 · Run time (min) = gallons ÷ flow rate (gal/min)
One inch of water spread over one square foot is 0.6234 gallons, so an inch of irrigation over a lawn multiplies quickly. Most lawns want about an inch of water per week (including rain), delivered in one or two deep soakings rather than daily sprinkles, which encourages deeper roots. Knowing your sprinkler’s flow rate turns the gallon figure into a run time you can set on a timer.
Worked example
Watering a 2000 ft² lawn with 1 inch: 2000 × 1 × 0.6234 = 1,247 gallons. At a 5 gal/min sprinkler that is 1247 ÷ 5 = 249 minutes, or about 4.2 hours (usually split across zones).
Frequently asked questions
How much water does a lawn need?
About 1 to 1.5 inches per week for most cool-season grasses, counting rainfall. Deep, infrequent watering (once or twice a week) builds stronger, deeper roots than daily light sprinkling.
How do I measure my sprinkler’s output?
Set a few straight-sided cans or rain gauges around the zone, run it for 15 minutes, and average the depth collected. Multiply by 4 to get inches per hour, which you can use to time an inch of water.
Why deep and infrequent?
Frequent shallow watering keeps roots near the surface where they dry out fast. Soaking deeply less often pushes roots down, making the lawn more drought-tolerant and resilient.
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This calculator is for educational purposes. Double-check important results before acting on them.