Irrigation Calculator
Calculate how long to run your lawn sprinklers to provide your grass with the recommended 1.0 inch of water per week. Prevents shallow root growth and wasteful water bills by splitting irrigation into two or three deep soaking cycles.
Total square footage of irrigated turf grass
Total weekly irrigation depth
Total flow rate across all active sprinkler heads in the zone (average residential zone is 8–15 GPM)
Total minutes the sprinkler zone must run over the course of a week
How to Use This Calculator
- Enter your lawn zone square footage.
- Select your weekly water target (1.0 inch is standard for most turfgrasses).
- Enter your sprinkler zone flow rate in Gallons Per Minute (GPM).
- Set your sprinkler controller timer to the recommended per-cycle minutes.
Formula & Calculation Methodology
Applying 1 inch of water over 1 square foot requires 144 cubic inches of water (144 ÷ 231 cu in/gal = 0.62338 gallons). Dividing total weekly volume by the sprinkler system’s flow rate determines operating minutes.
Worked Example
4,000 sq ft lawn needing 1.0 inch/week using 12 GPM sprinkler zone
Small 1,000 sq ft lawn at 1.0 inch/week using 8 GPM sprinkler
Frequently Asked Questions
How much water does a lawn need per week?↓
Most healthy established turfgrass varieties (such as Kentucky Bluegrass, Tall Fescue, and Bermuda) require approximately 1.0 to 1.5 inches of water per week (including natural rainfall) to maintain vibrant green growth.
What is the tuna can test for sprinkler output?↓
Place 4 or 5 empty tuna or cat food cans (which are about 1 inch deep) around your lawn. Run your sprinklers for 15 minutes, then measure the water depth with a ruler. If there is 1/4 inch of water in the cans, your system puts down 1 inch per hour.
What is the best time of day to water the lawn?↓
Early morning between 4:00 AM and 8:00 AM is the best time to irrigate. Winds are calm, water pressure is highest, and evaporation losses are minimal, allowing grass blades to dry quickly once the sun rises to prevent fungal diseases.
What is a limitation when setting a fixed irrigation timer?↓
Fixed timers don’t adjust for rainfall; installing an inexpensive smart Wi-Fi irrigation controller or rain shutoff sensor prevents wasting water during wet weather.
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Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.