Lawn Watering Calculator
Work out how much water your lawn needs and how long to run the sprinkler. Enter the lawn size and weekly depth, then add a can-test result, a zone flow rate or a precipitation rate, and get gallons or litres per week and the minutes per watering.
Lawn watering calculator
How to use the lawn watering calculator
- Measure the lawn. Enter the length and width, a diameter, or an area you know.
- Set the weekly water depth. About 1 inch (25 mm) a week is a common guide, counting rain. Use less in cool weather.
- Choose how to find sprinkler output. Use a can test (depth caught in a timed run), the zone flow rate, a known precipitation rate, or skip it to see volume only.
- Pick the number of watering days. Splitting the total over two or three days lets water soak in instead of running off.
- Read the schedule. You get gallons or litres per week, the run time per week, and the run time per watering.
Lawn watering formulas
Gallons = area (ft²) × depth (in) × 0.6234
Sprinkler rate (in/h) = can depth (in) × 60 ÷ test minutes = flow (gpm) × 96.25 ÷ area (ft²)
Run time (min) = depth ÷ rate × 60
An inch of water over a square foot is 144 cubic inches, and a US gallon is 231 cubic inches, which gives the 0.6234 factor. The 96.25 constant is the same relationship per gallon per minute over an hour. In metric the arithmetic is easy: one millimetre over one square metre is one litre.
Worked examples
Gallons for a lawn. 2,000 ft² at 1 inch is 1,247 gallons (4,720 litres) a week.
Can test. Cans caught 0.375 inch in 15 minutes: the sprinkler puts down 1.5 in/hour, so 40 minutes a week, or 20 minutes twice a week.
From the flow rate. A zone with 8 gpm over 2,000 ft² applies 8 × 96.25 ÷ 2,000 = 0.385 in/hour, so 1 inch needs 156 minutes a week. Split it into several short cycles.
Metric. 100 m² at 25 mm needs 2,500 litres a week.
Gallons by depth
| Depth | Gallons per 1,000 ft² | Litres per m² |
|---|---|---|
| ½ in (12.5 mm) | 312 | 12.5 |
| ¾ in (19 mm) | 468 | 19 |
| 1 in (25 mm) | 623 | 25 |
| 1½ in (38 mm) | 935 | 38 |
Watering well
Virginia Cooperative Extension recommends deep, infrequent watering that soaks the root zone, early in the morning. If water puddles after about 30 minutes, run shorter cycles. Use a rain gauge, subtract rainfall from your weekly target, and check sprinkler overlap and uniformity with the can test. Lawn needs rise in the hottest weeks and fall in cool weather.
Features
- Gallons, litres and cubic metres per week, with an optional water cost.
- Can-test, flow-rate and precipitation-rate modes.
- Run time per week and per watering, and a puddle tip for long cycles.
- Copy result, reset and a printable report in five themes on A4 or Letter.
Plan the rest of the lawn
Measure the lawn with the lawn area calculator, feed it with the lawn fertilizer calculator, seed bare patches using the grass seed calculator, and for water features try the pond volume calculator.
Frequently asked questions
How many gallons is 1 inch of water on a lawn?
One inch over one square foot is 0.623 gallons (144 ÷ 231), so 1 inch on 1,000 ft² is 623 gallons. In metric, 1 mm over 1 m² is exactly 1 litre.
How much water does a lawn need per week?
Virginia Cooperative Extension gives about 1 inch a week for most turfgrasses in warm conditions, from rain and irrigation together. Needs vary with grass, climate and soil.
How do I do a can test?
Place several straight-sided cans across the zone, run the sprinkler for a timed period such as 15 minutes, then average the depths. The time to apply 1 inch is the test minutes ÷ the average depth.
How long should I run my sprinkler?
If cans catch 0.375 inch in 15 minutes, the sprinkler applies 1.5 inches an hour, so 1 inch takes 40 minutes a week. Iowa State says to fill the cans to half an inch and double the time for 1 inch.
Why split watering into more than one session?
Most soils cannot absorb an inch at once. Virginia Cooperative Extension suggests smaller amounts every three to four days and stopping when puddles form.
Is it better to water deeply or often?
Deeply and less often. Deep watering encourages deeper roots and fewer weed seeds than light daily watering. Water early in the morning when evaporation and wind are lowest.
How much water does a tree need?
Iowa State uses 0.623 gallons per square foot per inch applied to the root zone. A root zone of 16 ft² needs about 10 gallons for 1 inch.
Related calculators
Lawn Fertilizer Calculator
Pounds of fertilizer and bags needed for your lawn from the N rate and bag analysis.
Lawn Area Calculator
Square feet and acres of an irregular lawn, with quick seed and fertilizer amounts.
Grass Seed Calculator
Pounds of grass seed for a new lawn or overseeding, by grass type.
Pond Volume Calculator
Gallons or litres in a pond, with pump flow and liner size.
Sources and references
About this calculator
Written and maintained by Rashid Mehmood, founder of CalcTen. The formulas are unit-tested against hand-worked examples, and the content is reviewed whenever product sizes or guidance change. Last updated 14 November 2026. See our editorial policy.
Results are estimates for planning and ordering. Coverage, soil and plant needs vary with site and product, so check labels and local advice, and follow the manufacturer's instructions for any chemical or fertiliser. Read the disclaimer.