Calculators Catch cup test
The catch cup test: how long to run your sprinklers
Nobody can tell you how many minutes your lawn needs, because it depends on how fast your particular sprinklers put water down. Fifteen minutes and a few tins gives you the real number, station by station.
Why bother: water deep, not often
Roots grow where the water is. A short sprinkle every day only wets the top few centimetres, so the roots stay up there too. That lawn browns off the first hot day you miss, and the constantly damp surface suits weeds and fungus.
A deep soak, then a few dry days, pulls the roots down after the water into cooler soil that stays moist for longer. Deep roots mean a lawn that handles the heat, needs less water overall, and crowds out weeds.
To water deep on purpose you need to know how much water your system actually puts down. That is all the catch cup test measures.
How to do the catch cup test
- Get 5 or 6 identical containers. Flat bottom, straight sides. Tuna tins or cat food tins are perfect. Cups that taper will give you the wrong reading.
- Spread them across one station. Some near the sprinklers, some in the middle, some at the edges. Not right up against a head.
- Run that station for 15 minutes. Use the manual run on your controller so the time is exact.
- Measure each one with a ruler, in millimetres. Stand the ruler in the tin and read where the water reaches.
- Average them. Add them all up and divide by the number of containers.
- Put the average and the 15 minutes into the calculator below. It tells you how long to run that station.
- Repeat for every station. Pop-up sprays and rotors put down very different amounts, so each station gets its own run time.
Worked example
Six tins after 15 minutes read 4, 5, 3, 4, 5 and 3mm. That adds up to 24mm, so the average is 4mm.
For a 10mm soak: 10 ÷ 4 × 15 = 37.5 minutes for that station. Its rate is 16mm an hour.
Work out your run time
10mm is a normal soak for an established lawn. Go higher on sand, lower on clay.
Your tins will not all match, and that gap matters more than the run time. If one has 8mm and another has 2mm, no run time fixes that. Sort the coverage first.
How often should I water my lawn?
Less often than you think. Give it a full soak, then wait until the lawn tells you it is thirsty: leaves folding or going dull blue-grey, or footprints staying flat. In a Perth summer on sand that is usually twice a week, your two rostered days. In spring and autumn it can be once a week or less.
How much water does a lawn need?
About 10mm per watering for an established lawn, which wets the root zone on sand without most of it draining away. Clay soils can take 15 to 20mm less often, as long as it is not running off. New turf and seed are the exception: little and often until the roots are in.
The longer version
Perth specifics
The sprinkler ban runs 1 June to 31 August every year. It is permanent, not a drought measure, and it covers bore water as well as scheme. Outside those months you get two rostered days based on your house number, so the run time matters more here than somewhere that can water whenever it likes.
Most of Perth is on sand, which drains fast and holds very little. Two shorter soaks usually beat one long one, because the excess on a long run is past the roots before the grass can use it.
Poor coverage
A big spread between containers means blocked, sunken or badly angled heads. You are either overwatering half the lawn to keep the other half alive, or wasting it. Winter is the time to run every station, check for that, and replace the controller battery, so the system works when the ban lifts.
Your lawn, every product, one number
This gives you a run time. It cannot tell you what to spray, or how much. The app already knows your lawn's size and grass type, so it turns any label rate into what actually goes in your sprayer or spreader. Log it once and it tells you when it is due again.
Free. No account. No Pro tier. Nothing is locked and nothing is paywalled, and your lawn data never leaves your phone.