US Lawn Watering
US Lawn Watering — US reference tool.
About US Lawn Watering
Turf watering in the US is measured in inches of water per week, the same unit as rainfall, which makes rain a direct credit against what you have to irrigate. Subtract the rain you already received from the weekly requirement to get the deficit, then convert: one inch of water over one square foot is 0.6234 US gallons. Runtime depends on your sprinkler's precipitation rate, which you measure by setting straight-sided cans around the zone and timing how long they take to fill to a known depth. When the deficit exceeds about three quarters of an inch the calculator splits it into two sessions, because most soils cannot absorb more than that in one pass without runoff.
Formulas
Irrigation deficit
Deficit (in) = weekly requirement - rainfall received
Volume
Gallons = deficit (in) x area (sq ft) x 0.6234
- 0.6234
- US gallons in one inch of water over one square foot
Runtime
Minutes = (deficit / sprinkler rate in/hour) x 60
Worked example
With the default values below, US Lawn Watering returns Water Needed This Week of 2,992. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Lawn areaaccepts 1–500,000 sq ft
- 4,000 sq ft
- Weekly water requirementaccepts 0.1–4 in
- 1.5 in
- Rainfall received this weekaccepts 0–10 in
- 0.3 in
- Sprinkler outputaccepts 0.05–3 in/hour
- 0.5 in/hour
Results
- Water Needed This Week
- 2,992 gal
- Total Sprinkler Runtime
- 144 min
- Minutes per Session
- 72 min
- Irrigation Deficit
- 1.20 in
Step by step
- 1Values used
- 2Irrigation deficit
- 3Volume
- 4Runtime
- 5Water Needed This Week= 2,992 gal
- 6Total Sprinkler Runtime= 144 min
- 7Minutes per Session= 72 min
- 8Irrigation Deficit= 1.20 in
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- An estimate for planning only. Many US municipalities and water districts impose watering-day restrictions, time-of-day rules, or drought surcharges. Check your local utility's current rules before setting an irrigation schedule.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
An estimate for planning only. Many US municipalities and water districts impose watering-day restrictions, time-of-day rules, or drought surcharges. Check your local utility's current rules before setting an irrigation schedule.
Frequently Asked Questions
How do I measure my sprinkler's output rate?
Place several straight-sided containers such as tuna cans across the zone, run the sprinkler for 20 minutes, then measure the average depth collected and multiply by three to get inches per hour. Averaging several cans also reveals uneven coverage.
Why split the week into two sessions?
Most soils absorb well under an inch of water before the rest runs off or puddles. Two deeper sessions per week encourage roots to grow down, whereas daily light watering keeps roots shallow and makes the lawn less drought-tolerant.
Does rainfall really count one-for-one?
Roughly, for steady soaking rain. A brief intense thunderstorm largely runs off, so credit only part of it. Rain gauges are cheap and far more reliable for this than a regional forecast total.
Related Calculators
United States specifics
- Currency
- $ USDUS Dollar
- Region
- North America
- Country code
- US
- Amounts look like
- $1,234,567.89
- Dates look like
- Mar 9, 2026
- Units
- imperialWeek starts Sunday
In United States, imperial units are in everyday use.
Results on this page are expressed in USD (US Dollar). Figures are estimates for general planning — confirm current rates and thresholds with the relevant United States authority before relying on them.