Lawn Watering Calculator
Watering advice is given as a depth, usually about an inch a week, but your hose and water bill are measured in gallons and minutes. Converting between them is exact arithmetic: one inch of water over one square foot is 0.6234 gallons, a figure that follows directly from the definition of the U.S. gallon. Enter your target depth, your lawn area, and your sprinkler's output rate, and this calculator returns the gallons needed and the run time to apply them, so you water the right amount without guessing.
Lawn watering formula
Gallons per inch per sq ft = 7.48052 / 12 = 0.6234
Gallons needed = depth * area * 0.6234
Volume in cubic feet = (depth / 12) * area
Run time = gallons needed / sprinkler output
Gallons per 1,000 sq ft = depth * 1,000 * 0.6234
The constant 0.6234 is exact: a U.S. gallon is 231 cubic inches, so a cubic foot is 7.48052 gallons, and one inch over a square foot is one twelfth of that.
Watering context
- The depth-to-gallons conversion is a definition, not an estimate, so it is exact for any lawn.
- Subtract recent rainfall from your target depth so you do not overwater.
- Watering deeply and less often encourages deeper roots than frequent shallow watering.
- Early morning watering reduces evaporation loss and disease risk.
- Measure sprinkler output with straight-sided cans if you do not have a flow specification.
Lawn watering calculator: frequently asked questions
How many gallons does it take to water my lawn?
One inch of water over one square foot is 0.6234 gallons, because a cubic foot holds 7.48052 gallons and one inch is one twelfth of a foot. Multiply your target depth in inches by your lawn area in square feet by 0.6234 to get the gallons needed. The calculator does this for you.
Where does the 0.6234 figure come from?
It is a pure unit conversion, not an estimate. The U.S. gallon is defined as 231 cubic inches, so a cubic foot (1,728 cubic inches) equals 7.48052 gallons. One inch of depth over a square foot is one twelfth of a cubic foot, which is 7.48052 divided by 12, or 0.6234 gallons.
How long should I run my sprinkler?
Run time equals the gallons needed divided by your sprinkler's output in gallons per minute. To measure your sprinkler output, place several straight-sided cans on the lawn, run the sprinkler for a set time, and measure the average depth collected, or read the flow rate from the sprinkler specification.
What weekly watering depth should I aim for?
The right depth depends on grass species, soil, and climate, and your state cooperative extension service publishes local guidance. Many cool-season lawns are watered to roughly an inch per week including rainfall. Because the right figure varies, this calculator takes the target depth as an input.
Should I subtract rainfall?
Yes. Enter the depth you still need to apply after accounting for recent rainfall. If your target is one inch per week and a half inch of rain fell, set the target to half an inch so you do not overwater, which wastes water and can promote shallow roots and disease.
Official sources
- NIST: U.S. gallon and cubic foot definitions.
- U.S. EPA WaterSense: Outdoor watering tips.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.