How Much Water Does a Lawn Need? Gallons per Inch and Sprinkler Run Times
October 21, 2026
Most lawn grasses need about one inch of water per week from rain and irrigation combined during the growing season, more in extreme heat and less in cool weather. One inch of water over one square foot is 0.623 gallons (since a square foot at 1 inch deep holds 144 cubic inches, and a gallon is 231 cubic inches). So a 5,000 square foot lawn needs 5,000 × 0.623 = 3,117 gallons per week to receive an inch.
Knowing how much water your sprinklers actually deliver tells you how long to run them. Many people water too often and too shallowly, which encourages shallow roots and wastes water.
Skip the math and get your answer instantly:
Open the Square Footage Calculator →The Gallons Formula
Gallons = area in square feet × inches of water × 0.623. A 1,000 square foot area gets 623 gallons per inch. A 5,000 square foot lawn gets 3,117 gallons per inch. A lawn that needs 1.5 inches in a hot week requires 4,675 gallons. At a water price of $5 per 1,000 gallons, an inch on 5,000 square feet costs about $15.60, and a 20-week season of weekly inches costs around $312, before sewer charges that may apply to outdoor water in some areas.
Your water bill may measure in cubic feet or hundred cubic feet (CCF); one CCF is 748 gallons.
| Lawn area | Gallons for 1 inch | Gallons for 1.5 inches | Cost at $5 per 1,000 gal (1 inch) |
|---|---|---|---|
| 1,000 sq ft | 623 | 935 | $3.12 |
| 2,500 sq ft | 1,558 | 2,337 | $7.79 |
| 5,000 sq ft | 3,117 | 4,675 | $15.58 |
| 10,000 sq ft | 6,230 | 9,345 | $31.15 |
Measure Your Sprinkler Output
Place several straight-sided containers, such as tuna cans or rain gauges, around the lawn in the sprinkler's area. Run the sprinkler for 15 minutes and measure the depth in each. Average the readings. If the average is 0.25 inches in 15 minutes, the sprinkler delivers 1 inch per hour, so it needs 60 minutes to supply an inch. Rotary heads typically deliver 0.4 to 0.6 inches per hour, impact sprinklers around 0.5 to 1 inch, and fixed spray heads 1.5 to 2 inches per hour.
Uneven readings show poor coverage; adjust the heads or spacing. The lowest-reading areas determine how long you have to run to avoid dry spots.
How Often to Water
Deep, infrequent watering produces stronger roots than frequent light watering. A common approach is to apply the weekly inch in two or three sessions rather than daily. If your sprinklers deliver 0.5 inches per hour, you would run for 60 minutes twice a week. Clay soils absorb water slowly, so split each session into cycles of 15 to 20 minutes with soak time between to avoid runoff. Sandy soils absorb quickly but hold less, so they may need more frequent watering.
Water early in the morning, when evaporation and wind are lower, and the grass dries during the day, which reduces disease.
Adjusting for Weather
Skip a session after a rain of half an inch or more. Use a rain gauge to track natural rainfall, and subtract it from the weekly target. Grass needs less in spring and fall, and more in midsummer heat. Signs of thirst include footprints that stay visible, a bluish-gray tint, and curled blades. Smart controllers that adjust to local weather can cut outdoor water use by 15% to 30%.
Reducing Water Use
Choose grass types suited to your climate, mow high (3 to 4 inches for most cool-season grasses) to shade the soil, leave clippings, aerate compacted soil, and consider replacing hard-to-water areas with native plants or mulch. Some regions have watering restrictions, so check local rules.
Frequently Asked Questions
How many gallons are in an inch of water over a lawn?
0.623 gallons per square foot, so 623 gallons per 1,000 square feet.
How much water does a lawn need per week?
Typically about one inch from rain and irrigation combined, more in extreme heat.
How do I know how long to run my sprinklers?
Measure output with cans for 15 minutes, then calculate the time needed to deliver the target depth.
When is the best time to water?
Early morning, before the heat and wind of the day.
Is it better to water more often or deeper?
Deeper and less often, to encourage deep roots.