Lawn Watering Calculator: Sprinkler Time and Gallons
How long should I water my lawn? Choose whether you know your sprinkler output (inches per hour) or measured it with a tuna-can test. Only the fields for the chosen method are used. Depth targets are typical values.
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Formula
- Output from tuna-can test:
rate (in/h) = depth in can / test minutes x 60 minutes = target depth / rate x 60gallons per week = area x depth x waterings x 144 / 231(1 inch over 1 sq ft = 0.6234 US gallons)
Worked example
Target 0.5 in, sprinkler output 0.5 in/h: 0.5 / 0.5 x 60 = 60 minutes. For 2,000 sq ft watered 3 times a week: 2,000 x 0.5 x 3 x 0.6234 = 1,870 gallons a week. With a tuna-can test of 0.25 in in 15 minutes the output is 1 in/h, so the run time drops to 30 minutes.
Another case: a 1 in target at 0.5 in/h takes 120 minutes, and one watering of 1,000 sq ft uses 623 gallons.
When to use it
Use it to turn a rule such as about 1 inch of water a week (a typical figure that includes rain) into a sprinkler run time. The tuna-can test is useful because sprinkler output varies a lot with pressure and nozzle type. Run the test in several spots and average them.
Common mistakes
- Using the sprinkler's rated output instead of measuring it.
- Running one long session on clay or sloped soil, where water runs off. Splitting it into shorter sessions often helps.
- Forgetting to subtract recent rain from the target depth.
- Mixing minutes and hours; the tool converts the rate to inches per hour.
How it differs from nearby calculators
The irrigation flow calculator is about pipes and emitters: flow per zone, how many emitters a supply can run, and runtime for drip systems. This lawn page is about sprinklers on grass. The rain barrel calculator shows how much rain you can collect to cover some of that water, and the lawn seed calculator is for the new grass that needs it.
Frequently asked questions
How long should I run my sprinkler?
Divide the depth you want by the sprinkler output and multiply by 60. For 0.5 in at 0.5 in/h that is 0.5 ÷ 0.5 × 60 = 60 minutes.
How does the tuna-can test work?
Place several flat-bottomed cans on the lawn, run the sprinkler for a set time and measure the average depth in them. 0.25 in in 15 minutes is 1 in/h, so a 0.5 in watering takes 30 minutes.
How much water does a lawn need per week?
A commonly quoted typical figure is about 1 inch per week including rain, but needs vary with grass, soil and weather. Adjust the target depth to suit your conditions.
How are gallons calculated?
One inch of water over one square foot is 144 cubic inches, which is 144 ÷ 231 = 0.623 US gallons. For 2,000 sq ft at 0.5 in, 3 times a week, that is about 1,870 gallons.
How long to run a sprinkler to put down 1 inch of water?
Divide the depth by the output and multiply by 60. At 0.5 in/h, 1 / 0.5 x 60 = 120 minutes.
How many gallons does it take to water 1,000 square feet 1 inch deep?
One inch over one square foot is 144 / 231 = 0.6234 US gallons. For 1,000 sq ft that is about 623 gallons.
How long to water with a tuna can test of 0.3 inch in 20 minutes?
The output is 0.3 / 20 x 60 = 0.9 in/h. To apply a typical 0.75 in you would run the sprinkler 0.75 / 0.9 x 60 = 50 minutes.