Lawn watering calculator
This lawn watering calculator turns a simple can test into sprinkler minutes. Set out flat cans, run the sprinkler for 15 minutes and measure the average depth. Nebraska Extension says lawns need about one inch of water per week, up to 1.5 inches in the hottest part of summer – the calculator tells you how long to run your sprinkler for that.
Example: Unit: Inches · Average depth in the cans 0.375 · Test run time 15 min · Water per week 1 → Run time per week: 40 minutes per week for 1 in. Source: Nebraska Extension (University of Nebraska–Lincoln), K. Feehan, Irrigation Audits Helpful (18 May 2022): lawns need about one inch of water per week, up to 1.5 inches in the hottest part of summer; 10–15 flat cans, run at least 15 minutes, average the cans; soil moist to about six inches; water deeply but infrequently (read 10.10.2026). Updated: .
How it is calculated
Lawns need about one inch of water per week, and up to one and a half inches in the hottest part of summer. That is the guide value of Nebraska Extension at the University of Nebraska–Lincoln. How long your sprinkler has to run for that depends on how much water it actually puts down – which a simple can test (tuna can test) measures.
How the can test works
- Place 10 to 15 flat-bottomed, straight-sided cans (tuna or cat food cans) uniformly 10 to 15 feet apart in the sprinkler zone.
- Run the system for at least 15 minutes; some systems need 30 minutes before there is a measurable amount in the cans.
- Measure the water in each can with a ruler, add the measurements and divide by the number of cans.
- Big differences between cans mean the area is not watered uniformly.
Example
| Average in cans | Test time | For 1 inch | For 1.5 inches |
|---|---|---|---|
| 0.375 in (3/8 inch) | 15 min | 40 min | 60 min |
| 0.25 in | 15 min | 60 min | 90 min |
| 0.5 in | 15 min | 30 min | 45 min |
The formula is run time = weekly amount ÷ (can depth ÷ test minutes): 1 ÷ (0.375 ÷ 15) = 40 minutes. This sprinkler puts down 1.5 inches per hour. One inch on 1,000 sq ft of lawn is about 623 gallons a week (1 inch × 1 sq ft = 144 cubic inches). Nebraska Extension recommends watering deeply but infrequently; ideally the soil is moist to a depth of about six inches.
How much seed an area needs is shown by the grass seed calculator; whether a rain tank can cover the demand by the rainwater harvesting calculator.
Frequently asked questions
How long should I water my lawn to get 1 inch?
It depends on your sprinkler. If the cans collect 3/8 inch in 15 minutes, you need 40 minutes per week for 1 inch.
How much water does a lawn need per week?
About one inch, up to 1.5 inches in the hottest part of summer, according to Nebraska Extension.
How many gallons is 1 inch of water on a lawn?
About 623 gallons per 1,000 sq ft, because one inch on one square foot is 144 cubic inches (0.623 gallons).
How often should I water?
Deeply but infrequently. The soil should be moist to about six inches.
How do I know if my lawn needs water?
If a screwdriver is hard to push into the soil, no soil sticks to it and it does not feel cool, the lawn needs water.
How many cans do I need for the test?
10 to 15 flat-bottomed, straight-sided cans; the more cans, the more accurate the result.
Sources and legal basis
- Nebraska Extension (University of Nebraska–Lincoln), K. Feehan, Irrigation Audits Helpful (18 May 2022): lawns need about one inch of water per week, up to 1.5 inches in the hottest part of summer; 10–15 flat cans, run at least 15 minutes, average the cans; soil moist to about six inches; water deeply but infrequently (read 10.10.2026)
- NIST SP 811, Appendix B.8: 1 in = 2.54 cm, 1 ft² = 0.092 903 04 m², 1 gal (U.S.) = 3.785 412 L (read 10.10.2026)
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