How to Measure Sprinkler Coverage With Catch Cups

A catch cup test, also called a catch can test, is the standard way to find out exactly how much water your sprinkler actually delivers and how evenly it spreads that water across your lawn. It takes about half an hour and needs nothing more than identical straight-sided containers, a ruler, and a working sprinkler.

Why guessing sprinkler output does not work

A sprinkler’s stated flow rate or box label tells you almost nothing about what your lawn actually receives, because real-world output depends on your water pressure, nozzle wear, spacing, and overlap with neighboring heads or pattern. Two identical sprinklers on two different homes can deliver noticeably different amounts of water. A catch cup test measures your actual setup instead of relying on a manufacturer estimate.

What you need

• 6 to 10 identical straight-sided, flat-bottomed containers of the same size, such as tuna cans, cat food cans, or purpose-made rain gauges. Straight sides matter because tapered cups distort the depth reading.
• A ruler or measuring tape marked in tenths or sixteenths of an inch.
• A timer or stopwatch.
• Your sprinkler and hose or irrigation zone, set up exactly as it runs normally.

Step 1: Place the cups across the watering pattern

Set the cups out in a grid or straight line across the area the sprinkler covers, spacing them evenly from close to the sprinkler head out to the edge of its throw. For an oscillating sprinkler, place cups along the full length of the fan pattern since output typically varies from the center to the ends. For a rotor or impact sprinkler covering a circle, place cups along a line from the head out to the maximum radius.

Step 2: Run the sprinkler for a fixed, known time

Turn on the sprinkler and let it run for a set period, commonly 15, 20, or 30 minutes. Keep the time consistent across the whole test since you will use it to convert the collected depth into an hourly rate. Avoid research on a windy day, since wind will blow the pattern off the cups and skew your results.

Step 3: Measure the depth in each cup

After the timer stops, measure the water depth in each cup with your ruler, recording each reading to the nearest sixteenth or tenth of an inch. Do this immediately, before evaporation or spillage changes the readings.

Step 4: Calculate the average output rate

Add up all the depth readings and divide by the number of cups to get the average depth collected during your test period. Then convert to an hourly rate: if your test ran 20 minutes and the average depth was one sixth of an inch, multiply by 3 to get roughly 0.5 inches per hour. Use this hourly figure with our lawn watering time calculation guide to set an accurate run time going forward, or plug it directly into how long you should run the sprinkler per our sprinkler run time guide.

Step 5: Check uniformity, not just the average

The average tells you how much water fell overall, but the spread between your highest and lowest cup readings tells you how evenly it fell. A large gap between the wettest and driest cups means parts of your lawn are being overwatered while others are underwatered, even though the average looks fine. Significant unevenness usually points to incorrect spacing between sprinkler heads, wind distortion, low or fluctuating pressure, a worn or partially clogged nozzle, or a sprinkler that is not rotating through its full pattern; see our guides on a stuck oscillating sprinkler or a non-rotating impact sprinkler if a specific area consistently reads dry.

What to do with uneven results

If certain cups consistently read much lower, try adjusting the sprinkler’s position, overlapping the pattern of a second sprinkler head to cover the gap, or switching to a sprinkler style better suited to your lawn’s shape, such as the options in our sprinklers for narrow and rectangular lawns guide. Retest after any adjustment to confirm the change actually improved coverage rather than assuming it did.

How often to repeat the test

A catch cup test is not a one-time chore. Nozzles wear, sprinkler heads drift out of alignment after being bumped, and your household water pressure can shift over time. Repeating the test once or twice a growing season, and again any time a section of lawn looks noticeably drier or greener than the rest, keeps your watering schedule based on real, current data instead of an assumption from months earlier.