Craft Quantities
Plan & Takeoffs

Landscaping & Outdoor

Catch-Can Test Uniformity and Rate Calculator

A zone's measured precipitation rate and low-quarter distribution uniformity from a catch-can test, with the run-time multiplier the uniformity implies.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
Add every can's measured catch together and divide by the number of cans.

Measure each can into the same graduated cylinder, one at a time, and record every reading before averaging — the individual figures are what the low quarter is drawn from, and an average alone cannot produce a uniformity number. Empty and reseat any can that was knocked over rather than guessing at its reading.

Tools needed: Graduated cylinder, Identical catch cans, Stopwatch or controller run log

Sort the readings, take the driest quarter of them, and average just those.

Rank every can from lowest to highest, count off a quarter of them from the dry end, and average that subset. If the count does not divide by four, round the size of the subset up so the driest ground is fully represented — the whole point of the low quarter is that it describes the part of the lawn that decides how long the valve must run.

The internal diameter of the opening each can collects through.

Measure the aperture, not the body of the can — a tapered can catches through its rim, and using the wider base area understates the rate. For a square or rectangular device, work out its throat area and convert that to the diameter of a circle with the same area before entering it here.

How long the zone ran while the cans were collecting.

Long enough that the volumes are readable and short enough that nothing evaporates or overflows. Time the valve rather than the controller programme, since a station that takes several seconds to pressurise is not applying water for the whole of its nominal run.

How many catch devices were set out across the zone.

The grid has to sample the overlap between heads, not just the ground beside each one, so cans go out on a regular spacing across the whole zone rather than clustered where it is convenient. A sparse grid produces a uniformity figure with wide error bars, and the number that gets argued about later is usually the one taken from too few cans.

Measured precipitation rate

1.321 in/h

High confidence

The driest quarter of the ground is receiving a high proportion of the average, so run times set from the average will not leave dry patches behind.

Low-quarter distribution uniformity
76.47 %
Average catch depth over the test run
0.33 in
Run-time multiplier implied by the uniformity
1.31 multiplier
Throat area of one can
0.09 ft²
Cans forming the low quarter
6 cans
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • ISO 15886-3, Agricultural irrigation equipment — Sprinklers — Part 3: Characterization of distribution and test methods — sets out how sprinkler distribution is characterised under test
  • ASABE/ICC 802, Landscape Irrigation Sprinkler and Emitter Standard — the reference frame for the published nozzle data a catch-can test is checking against
  • Low-quarter distribution uniformity = mean catch of the lowest-scoring quarter of the cans ÷ mean catch of all cans; measured rate = mean catch volume ÷ can throat area ÷ test duration
  • Catch volumes are entered in millilitres because that is the graduation a catch-can audit is read at in every market — the millilitre here belongs to the method rather than to a display preference, in the same way that a fixed test area belongs to the test that defines it

Inputs used

Average Catch Volume Across All Cans (mL)
68
Average Catch of the Lowest Quarter of Cans (mL)
52
Catch Can Throat Diameter
4 in
Test Run Duration (minutes)
15
Number of Cans in the Grid
24

Intermediate steps

Low-quarter distribution uniformity
76.47 %
Average catch depth over the test run
0.33 in
Run-time multiplier implied by the uniformity
1.31 multiplier
Throat area of one can
0.09 ft²
Cans forming the low quarter
6 cans
Final result1.32 in/h

Confidence note: The driest quarter of the ground is receiving a high proportion of the average, so run times set from the average will not leave dry patches behind.

What this calculation does not cover

  • Describes the conditions on the day. Wind, supply pressure and a partially blocked nozzle all move the result, and a test run at dawn does not describe a zone that normally waters at midday.
  • A grid too sparse to sample the overlap between heads reports a uniformity that is mostly noise, whatever the arithmetic says.
  • Measures what lands in the cans, not what enters the soil. Runoff, interception by planting and infiltration limits are separate questions.

Add the equipment this sizes

This result is a specification — 1.321 in/h — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

4 in
Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations4
  1. ISO 15886-3, Agricultural irrigation equipment — Sprinklers — Part 3: Characterization of distribution and test methods — sets out how sprinkler distribution is characterised under test
  2. ASABE/ICC 802, Landscape Irrigation Sprinkler and Emitter Standard — the reference frame for the published nozzle data a catch-can test is checking against
  3. Low-quarter distribution uniformity = mean catch of the lowest-scoring quarter of the cans ÷ mean catch of all cans; measured rate = mean catch volume ÷ can throat area ÷ test duration
  4. Catch volumes are entered in millilitres because that is the graduation a catch-can audit is read at in every market — the millilitre here belongs to the method rather than to a display preference, in the same way that a fixed test area belongs to the test that defines it

Which documents these citations point at

Standards referenced: ISO 15886-3 (International Organization for Standardization, International); ICC 802 (International Code Council, United States).

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

  • Fixing Dry Spots in a Lawnuses this calculator

    The same patch browns every August. Cans on a grid separate a run-time fault from a spacing, pressure or soil fault before anything is bought.

Still deciding? Irrigation Zoning vs Distribution Uniformity — the factors that actually differ, with no invented prices.

How to calculate catch-can test uniformity and rate in 6 steps

  1. Average Catch Volume Across All Cans (mL)Add every can's measured catch together and divide by the number of cans.
  2. Average Catch of the Lowest Quarter of Cans (mL)Sort the readings, take the driest quarter of them, and average just those.
  3. Catch Can Throat DiameterThe internal diameter of the opening each can collects through.
  4. Test Run Duration (minutes)How long the zone ran while the cans were collecting.
  5. Number of Cans in the GridHow many catch devices were set out across the zone.
  6. Measured precipitation rateThe tool computes the measured precipitation rate from those figures and shows the formula, its sources, and a confidence rating alongside it.

Measured precipitation rate by catch can throat diameter

Page defaults, not your figures above.

Catch Can Throat DiameterMeasured precipitation rate (in/h)
2 in5.28
3 in2.35
4 in1.32
5 in0.845
6 in0.587
7 in0.431

Frequently asked questions

Why the lowest quarter rather than the lowest single can?
Because one can is an anecdote. A single low reading can come from a can that was knocked, shaded by a shrub, or sitting in the one spot a passing arc misses; averaging the driest quarter keeps the measure sensitive to genuinely dry ground while stopping a single outlier from condemning the zone. It is the measure the irrigation industry settled on precisely because it survives one bad can.
How does the measured rate differ from the catalogue figure?
Published nozzle data is laboratory data at a stated pressure, in still air, at a stated spacing. Your zone has the pressure the supply actually delivers, the spacing the site allowed, the wind that blows at the hour you irrigate, and whatever the last repair left behind. The grid measures all of that at once, which is why a commissioning figure is worth more than a designed one.
What do I do with the run-time multiplier?
Use it to see the cost of poor uniformity before you accept it. Multiplying the run time keeps the driest quarter alive, but it applies that same multiple everywhere else, so a mediocre uniformity turns directly into a water bill. On a zone that measures poorly, spend the effort on spacing, arc adjustment and matched nozzles first, and only fall back on the multiplier once the pattern is as good as the layout allows.
Should the cans go where the heads are, or between them?
Both, on a regular grid that ignores where the heads happen to be. A single head's own pattern is always heaviest near it, and the whole design premise of head-to-head coverage is that adjacent patterns average each other out. A grid placed to sample that overlap tells you whether the averaging is actually happening; a grid placed beside each head only tells you the heads are running.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.