How this calculator works
Grass wants a certain depth of water each week, no matter how it arrives. An inch of water on a square foot of lawn is 144 cubic inches, which is 0.623 gallons. So the weekly volume is the area times the inches times 0.623. How long that takes depends on the sprinkler: the inches it puts down each hour is its precipitation rate.
Worked example: a 5,000 ft² lawn that needs 1 in a week takes 5,000 × 1 × 0.623 = 3,117 gallons. Watered twice a week, each time puts down half an inch. A sprinkler that delivers 1 in an hour would run for 30 minutes each time (60 minutes a week). At $5 per 1,000 gallons, that is $15.58 a week.
Minutes to run per watering (2 waterings a week)
For different sprinkler outputs and weekly targets. Spray heads are often 1.5 to 2 in/hour, and rotors around 0.5.
| Sprinkler output | 1 inch a week | 1.5 inches a week |
|---|---|---|
| 0.5 in/hour | 60 min | 90 min |
| 1 in/hour | 30 min | 45 min |
| 1.5 in/hour | 20 min | 30 min |
| 2 in/hour | 15 min | 23 min |
Tips before you buy
- Water deeply and not often. Two or three long waterings a week grow deeper roots than a short one every day, and cope better with heat.
- Water early in the morning, before about 10 am, when the air is cool and calm. Less is lost to evaporation, and the grass dries during the day, which helps to prevent disease.
- Find out your own sprinkler rate with the can test: set several straight-sided cans around the lawn, run the sprinkler for 15 minutes, and measure the water in each. Multiply the average depth by 4 to get inches per hour.
- If water runs off before the time is up (on a slope or on hard clay soil), water in two or three shorter cycles an hour apart, so that it can soak in.
- The lawn tells you when it needs water: it turns a dull blue-gray, and footprints stay flattened. Skip a watering after a good rain, and use a rain gauge to check.
- A rain sensor or a smart controller that skips watering when rain is coming pays for itself over a summer.
Tools & materials for this project
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Frequently asked questions
How long should I water my lawn?
Enough to put down about 1 inch of water a week, split into two or three waterings. With a sprinkler that puts down an inch an hour, that is 20 to 30 minutes each time. Time it with a can test for your own sprinkler.
How many gallons does it take to water a lawn?
0.623 gallons per square foot for each inch of water. A 5,000 ft² lawn needs about 3,100 gallons for 1 inch.
How do I measure my sprinkler output?
Put out straight-sided cans, run the sprinkler for 15 minutes and measure the depth in each. The average depth in inches times 4 is the inches per hour. Or divide 96.25 times the gallons per minute by the area watered.
Is it better to water the lawn every day?
No. Frequent shallow watering keeps the roots near the surface. Watering two or three times a week, enough to wet the soil several inches down, encourages deeper roots and a tougher lawn.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.