Lawn Watering Calculator
How long to run a sprinkler each time to give your lawn the water depth you want a week, from a catch-cup test or the flow rate, and the water it uses.
Result…
How it's calculated
Rate = depth in the cups ÷ test minutes (or flow ÷ lawn area) Minutes per session = (water per week ÷ sessions) ÷ rate Water used = area × depth (1 mm over 1 m² = 1 L; 1 in over 1 ft² = 144 ÷ 231 US gal)
A lawn's water is measured as a depth, like rainfall. A catch-cup test measures what your sprinkler actually puts down: set several straight-sided cups or tins across the lawn, run it for a set time, and average the depths. With a flow rate instead, the calculator spreads the water over the whole area, which assumes nothing lands off the lawn. Units are exact: 1 mm over 1 m² is 1 litre, and 1 inch over 1 square foot is 144 cubic inches, or 144 ÷ 231 US gallons. The target depth is yours to choose: it depends on the grass, soil, season and your local rainfall.
Your numbers, step by step
About the Lawn Watering calculator
This lawn watering calculator tells you how many minutes to run a sprinkler each session to give your lawn the depth of water you aim for each week, and how much water that uses. Lawn water is measured as a depth, like rainfall, in millimetres or inches. You find your sprinkler's rate with a catch-cup test, setting cups or tins across the lawn and measuring the depth collected in a set time, or from its flow rate in litres or US gallons per minute. Then choose how many sessions a week to split the water into. The weekly depth is your own choice, because it depends on the grass, soil, season and local rainfall, and the calculator does not assume one. It works in metric or imperial, and every step is shown with your numbers. To measure an odd-shaped lawn, use the square footage calculator.
How to use it
- Choose “Metric” or “Imperial” and enter the “Lawn area”.
- Enter your target “Water per week” as a depth.
- Under “Sprinkler rate from”, choose “Catch-cup test” and enter the “Depth collected in the cups” and the “Test run time”, or choose “Flow rate”.
- Enter the number of “Sessions per week”.
- Read the “Minutes per session”, the watering rate and the water used per session and per week.
Worked example
In a catch-cup test, a sprinkler puts 6 mm into the cups in 20 minutes, a rate of 6 ÷ 20 = 0.3 mm a minute, or 18 mm an hour. To give an 80 m² lawn 25 mm a week in 2 sessions, each session is 12.5 mm, which takes 12.5 ÷ 0.3 = 41.7 minutes, about 83 minutes a week. The lawn uses 80 × 25 = 2000 litres a week. In imperial, a hose sprinkler running 5 US gallons a minute over 2000 ft² puts down about 0.24 inches an hour, so 1 inch a week in 2 sessions takes about 125 minutes each and uses about 1247 US gallons a week.
Updated
Questions people ask
How long should I run my sprinkler?
Divide the depth you want each session by your sprinkler's rate. If it puts down 0.3 mm a minute and you want 12.5 mm, run it for about 42 minutes.
How do I do a catch-cup test?
Place several straight-sided cups or tins around the area the sprinkler covers, run it for a set time such as 15 or 20 minutes, measure the depth in each and take the average. That average divided by the minutes is your rate.
How much water does a lawn need each week?
It depends on the type of grass, the soil, the season and how much rain falls, so take local advice or watch how your lawn responds. The calculator uses whatever weekly depth you enter.
How much water does watering the lawn use?
One millimetre over one square metre is one litre, and one inch over one square foot is 144 ÷ 231, about 0.62, US gallons. Multiply by the area and the depth. The volume converter turns litres into gallons.
Why is the flow-rate method less exact than a cup test?
It assumes all the water lands evenly on the lawn. Real sprinklers overlap, miss corners and throw some water onto paths, so a catch-cup test measures what the grass actually gets.
What if water runs off before the time is up?
Split the session into shorter runs with a break between them, so the soil has time to soak the water up. The total minutes stay the same.