Lawn Watering Calculator

Tell us how much water your lawn needs and how fast your sprinklers put it down, and we'll show exactly how long to run them.

📖 How it works & FAQ

Water to apply (inches)

Sprinkler output (inches / hour)

How long should you run your sprinklers?

Most cool-season lawns want about 1 to 1.5 inches of water per week, delivered in one or two deep soakings rather than daily sprinkles. The trouble is that "one inch" is a depth, not a time — and every sprinkler lays water down at a different speed. This calculator turns the depth you want into an exact number of minutes using one simple rule: minutes = inches ÷ rate × 60, where the rate is your sprinkler's output in inches per hour.

The catch-can test

To find your real output rate, set 3 to 5 straight-sided cans (tuna or cat-food tins work) around one zone, run the sprinklers for 15 minutes, then measure the average depth caught. Multiply that average by 4 to get inches per hour. A reading of 0.125 in over 15 minutes means a 0.5 in/hr rate. Every zone can differ, so test them separately and re-run the numbers for each.

How to use it

Enter the depth of water you want to apply, in inches (1 inch is a common weekly target).
Enter your sprinkler output in inches per hour from your catch-can test.
Read the run time — total minutes and the same figure as clock time — and set your timer to match.
Repeat for each zone that waters at a different rate.

These are general estimates to guide your timer, not professional agronomy or irrigation advice — adjust for your soil, grass type, and local rules.

FAQ

Should I water all at once or split it up?: On clay or sloped lawns, split the run into two shorter cycles so water soaks in instead of running off. The total minutes stay the same.
How much water does my lawn actually need?: Roughly 1 to 1.5 inches per week including rain. In hot spells lean higher; in cool or rainy weeks, less.
My zones water unevenly — what do I do?: Run a separate catch-can test per zone and calculate each one on its own rate, since spray heads and rotors differ a lot.
What's the best time of day to water?: Early morning, before about 10 a.m., so less evaporates and the blades dry out before nightfall, which reduces disease.