Sprinkler Catch-Cup Audit Calculator

Compare four catch-cup depths and estimate average application rate from a timed test.

Inputs

Preset: 15 min sprinkler test

Example catch depths of 0.25, 0.30, 0.35 and 0.30 in after 15 minutes. Replace them with measurements; four cups are a simplified check rather than a complete irrigation audit.

Catch cup 1 depth

Catch cup 2 depth

Catch cup 3 depth

Catch cup 4 depth

Formula, inputs and conditions

Formula: min(Catch cup 1 depth,Catch cup 2 depth,Catch cup 3 depth,Catch cup 4 depth)/((Catch cup 1 depth+Catch cup 2 depth+Catch cup 3 depth+Catch cup 4 depth)/4)

Decimal results are displayed to two places when needed.

Inputs: Four catch depths measured in the same unit, plus test duration for application-rate mode.
Outputs: Application rate in inches per hour and a simplified four-cup uniformity ratio.
Conditions and scope: Use four equally weighted observations from the test area. The lowest cup represents one quarter of these four samples; the tool does not process a larger audit sample or replace a full field audit. Results are planning estimates, not engineering, permit, code or contractor-price decisions.

Read depth and distribution from catch cups

Equal catch cups placed in a test area show how evenly water is distributed. This simplified four-cup calculation compares the lowest depth with the mean; with four equally weighted samples, one cup is the lowest quarter. Application rate uses the average depth and test duration.

Measure and calculate

Run a timed test and record all four catch depths using the same unit.
Choose uniformity ratio to compare the lowest catch with the average.
Choose application rate to convert average depth into inches per hour.

Calculation method

Four-cup uniformity ratio = minimum catch depth ÷ average catch depth.

A worked example

Inputs: A 15 minute test records depths of 0.25, 0.30, 0.35 and 0.30 in.
Calculation: Mean depth: 1.20 ÷ 4 = 0.30 in. Ratio: 0.25 ÷ 0.30 = 0.833333. Rate: 0.30 ÷ 15 × 60 = 1.2 in/hour.
Result: 0.83 ratio (0-1)

The initial ratio is 0.83, about 83.3%. Four observations are a simplified comparison and do not replace a full field audit. If every cup is dry, the ratio is undefined rather than zero.

Read the result

Output interpretation and next steps
Output or check	What it means for your project
Four-cup ratio: 0–1	The lowest catch divided by the four-cup mean gives a simplified uniformity ratio. Multiply by 100 to express the ratio as a percentage.
Application rate: in/hr	The mean depth divided by test time is scaled to one hour. This is separate from distribution uniformity.
Sampling limit	Four cups are a simplified comparison, not a full field audit. An all-dry test has no defined uniformity ratio because the mean is zero.

Common questions

Does a high average depth prove even watering?

No. Average application and uniformity answer different questions. Large differences between individual cups can be hidden by an average.

Can I calculate a ratio when every cup is empty?

No. The average is zero, so division is undefined. Check the test setup and repeat the measurement.