Free tool
Lawn watering calculator
How long to leave the sprinkler on, worked out from what it actually puts down rather than from a number off the internet.
Your sprinkler
Measure what it puts down
Put four or five straight-sided tins around the lawn, run the sprinkler for a set time, then measure the depth in each and take the average.
Measure the sprinkler, or type what it puts down, and the run time appears here.
Why measuring beats guessing
Every watering guide talks in millimetres, and no sprinkler is labelled in them. Between the nozzle, the pressure at your tap and how far apart the heads sit, two setups on the same street can differ threefold. A sum built on someone else's sprinkler is a sum about someone else's lawn.
The tins fix that in twenty minutes, and they tell you something no calculator can: how evenly it lands. If one tin holds twice what another does, no run time will keep the whole lawn happy, and moving a head is worth more than any amount of arithmetic.
Deep and less often
Roots grow to where the water is. A light daily sprinkle keeps them in the top centimetre, where the soil dries first and the lawn is at its most fragile in a hot week. A longer soak every few days sends them down, and a deeper lawn is the one that survives the fortnight you forget about it.
If water pools or runs off before the time is up, split it: half now, half an hour later. Heavy clay and slopes take water far more slowly than they look like they should.
Questions people ask
- How long should I run my sprinkler?
- Long enough to put down the depth your lawn needs, which depends entirely on how fast your sprinkler delivers water. A sprinkler laying 12 mm an hour needs 50 minutes to put down 10 mm. Two sprinklers on the same tap can differ threefold, so the only honest answer comes from measuring yours.
- How do I measure what my sprinkler puts down?
- Put four or five straight-sided tins around the lawn, a tuna tin is the classic, run the sprinkler for twenty minutes, then measure the depth in each and average them. Multiply by three for the hourly rate. The spread between tins matters as much as the average, because it shows the dry corner.
- How much water does a lawn need a week?
- Commonly quoted figures sit between 25 and 40 mm a week in summer, but the honest number depends on your grass, your soil, your shade and what the sky has already delivered. Watering deeply and less often grows deeper roots than a daily sprinkle.
- How many litres is a millimetre of water?
- One millimetre over one square metre is one litre. So 10 mm on 200 square metres is 2,000 litres, which is a useful figure when your water is tanked or metered.
- Should I water in the morning or the evening?
- Early morning. The leaf dries as the day warms, which gives fungus less time on a wet blade, and less is lost to wind and heat than at midday.
Stop typing your lawn size in
Trace your lawn once from the satellite view and every section is measured for you. Free, and it builds the schedule around your grass, your season and your local weather.