Lawn Watering Calculator
Wondering how long should I water my lawn each week? Enter your lawn's size, how much water it needs, and your sprinkler's output, and this free lawn watering calculator tells you exactly how many minutes to run your sprinklers per watering day — plus your total weekly runtime and gallons used. Results update instantly as you type.
Enter your numbers
Your results
| Breakdown | Value |
|---|---|
| Water needed | — |
| Sprinkler rate | — |
| Watering days | — |
| Sessions per day needed | — |
Estimated runtime: based on the widely used 1 inch-per-week guideline. Actual needs vary by grass type, soil, weather, and local watering rules — subtract rainfall and use the catch-cup test to calibrate.
How to use this calculator
Start with your lawn area in square feet — measure only the ground your sprinklers actually cover. Then enter how much water your lawn needs per week: 1 inch is the standard guideline (and you should subtract any rainfall you received).
Next, enter your sprinkler's precipitation rate in inches per hour. If you don't know it, the default of 0.5 in/hr is a reasonable estimate for rotor sprinklers; see the catch-cup test in the FAQs below for an exact number. Finally, choose watering days per week — 2 or 3 days is ideal for most lawns.
The results update instantly: runtime per watering day is the headline number to program into your controller or hose timer, and the gallons per week figure helps you estimate your water bill.
How it works
The math is straightforward: hours per week = inches of water needed ÷ sprinkler rate (in/hr), so 1 inch ÷ 0.5 in/hr = 2 hours per week. Dividing by watering days gives the per-session time: 2 hours ÷ 3 days = 40 minutes per session.
Water volume uses a fixed constant: one inch of water over one square foot equals 0.623 gallons (1 sq ft × 1/12 ft × 7.48052 gal/cu ft), so gallons per week = lawn area (sq ft) × inches needed × 0.623. For the defaults (1,000 sq ft, 1 inch), that's 1,000 × 1 × 0.623 = 623 gallons per week.
The "sessions per day" row splits long run times into chunks: many controllers and hose-end sprinklers perform better with two back-to-back cycles separated by 30–60 minutes (so water soaks in instead of running off), so if one session exceeds about an hour, it suggests splitting it. The 1 inch-per-week figure is a general guideline, not a hard rule: cool-season grasses like fescue and bluegrass typically want 1–1.5 inches in summer, warm-season grasses like bermuda often do fine with 0.75–1 inch, and any week with heavy rain needs less or none at all.
Frequently asked questions
How long should I water my lawn?
As a general rule, most lawns need about 1 inch of water per week, including rainfall. With a typical sprinkler that delivers 0.5 inches per hour, that works out to about 2 hours of total run time per week — for example, three 40-minute sessions. Enter your own lawn size, water need, and sprinkler rate above to get your exact number.
Is it bad to water my lawn every day?
Yes, daily watering is usually worse for your lawn. Short daily sprinkles wet only the surface, which encourages shallow roots that dry out faster. Watering deeply 2-3 times per week trains roots to grow deeper, making the grass more drought-tolerant. The exception is brand-new seed or sod, which does need light daily watering until it is established.
How do I find my sprinkler's precipitation rate?
Do a catch-cup test: place 5-6 empty tuna cans or rain gauges around one sprinkler zone, run the sprinklers for 20 minutes, then measure the water depth in each can. Average the depths, then multiply by 3 to get inches per hour (since 20 minutes is one-third of an hour). Most spray heads deliver 1-1.5 in/hr, while rotors deliver 0.3-0.5 in/hr. This calculator defaults to 0.5 in/hr, a common middle value.
How many gallons does it take to water my lawn?
One inch of water spread over 1,000 square feet equals about 623 gallons. The formula is gallons = lawn area (sq ft) x inches of water x 0.623. So a 5,000 sq ft lawn receiving 1 inch per week uses roughly 3,115 gallons per week. The calculator above shows your total automatically.
What is the best time of day to water my lawn?
Early morning, roughly 5-10 AM, is the best time to water. Wind and heat are low so less water evaporates, and the grass blades dry off after sunrise, which reduces fungus and disease risk. Avoid watering in the evening: grass that stays wet overnight is more prone to disease.