Sprinkler Uniformity & Does Every Plant Get a Fair Share?
Rates evenness
Enter your catch-can depths to get the Christiansen Uniformity Coefficient (CU), the mean application depth and a clear uniformity rating.
Enter your catch-can readings
Next: aim for CU ≥ 84% (excellent); your 90.9% is excellent. If low, check spacing, nozzle wear, pressure and wind drift, then re-test.
CU = 100 × (1 − Σ|xi − mean| ÷ (n × mean)); a denser catch-can grid gives a more reliable reading. Test in low wind.
Sprinkler uniformity — key facts
- CU
- 100 × (1 − mean dev ÷ mean)
- Excellent
- CU above ~84%
- Good
- CU ~75–84%
- Wasteful
- CU below ~70%
- Test
- Catch cans on a grid
- Best timing
- Calm air, early morning
- Improves
- Less water for same coverage
- Privacy
- Runs in your browser; nothing uploaded
One number for how evenly you water
A sprinkler system is only as good as its evenness. If some plants get a downpour while others stay dry, you are forced to over-water the whole field just to keep the dry corners alive — wasting water, energy and nutrients. The Christiansen Uniformity Coefficient turns a simple catch-can test into one honest number: CU = 100 × (1 − mean deviation ÷ mean), where higher means more even. Above about 84% is excellent; below 70% is leaving water and yield on the table.
This tool takes your catch-can depths and returns the mean application depth, the CU percentage, a plain-language rating and the number of cans you tested. Use it to audit a new install, to diagnose dry stripes between laterals, or to prove a system tune-up actually helped. Pair it with the Sprinkler System and Nozzle Discharge tools to design spacing and pressure that hold uniformity high.
Find the dry spots
Catch cans reveal where coverage falls short.
One honest number
CU rates evenness on a clear 0–100% scale.
Save water
Better uniformity means less total applied.
Prove a tune-up
Re-test to confirm a fix really raised CU.
Frequently Asked Questions
What is the Christiansen Uniformity Coefficient (CU)?+
CU is a single number that rates how evenly a sprinkler system spreads water across the field. It comes from a catch-can test: you place cans on a grid, run the sprinklers, and measure the water depth in each. CU = 100 × (1 − mean deviation ÷ mean depth), so 100% would be perfectly even and lower values mean some areas get much more or less than others.
How do I run a catch-can test?+
Set out identical catch cans on a regular grid across the wetted area, run the system for a set time, then measure the depth collected in each can. Enter all the depths into this tool and it computes the mean depth, the average deviation from that mean, and the CU. More cans on a finer grid give a more reliable result.
What is a good CU value?+
As a rule of thumb, a CU above about 84% is excellent, 75–84% is good, 70–75% is fair, and below about 70% wastes water and stresses parts of the field. Solid-set and centre-pivot systems can reach high CU; hand-move and poorly spaced laterals often fall short.
Why does uniformity matter?+
If water lands unevenly, you must over-irrigate the wettest zones to keep the driest ones adequately watered. That wastes water and energy, leaches nutrients in the wet spots and stresses crops in the dry spots. Improving CU lets you apply less total water while still meeting the crop's needs everywhere.
What is the difference between CU and DU?+
CU (Christiansen) uses the average deviation from the mean across all cans. Distribution Uniformity (DU) instead compares the average of the lowest quarter of catches to the overall average, so it focuses on the driest areas. Both describe evenness; CU is the classic sprinkler figure and is what this tool reports.
What causes poor sprinkler uniformity?+
Common causes are sprinklers spaced too far apart, wrong nozzle sizes, pressure that is too low or varies along the lateral, wind drift, worn or partly blocked nozzles, and tilted or sunken risers. A catch-can test plus this CU figure helps you find and fix the weak spots.
How many catch cans should I use?+
More is better, but a practical test uses a grid of at least 16 to 24 cans spread evenly across one or more sprinkler spacings. Use identical containers, place them at a consistent height, and read them promptly after the run so evaporation does not bias the lower catches.
How does wind affect the test?+
Wind blows spray downwind, so cans on the windward side under-catch and those downwind over-catch, lowering the measured CU. Run the test in calm conditions, ideally early morning, for a fair reading. A system that tests well in calm air will still lose uniformity on windy days, so plan irrigation timing accordingly.
Is this CU reliable for an irrigation audit?+
The CU formula is exact for the depths you enter, so the maths is reliable. The accuracy depends on a sound catch-can test — enough cans, identical containers, calm conditions and careful reading. For a formal audit, repeat the test across several sprinklers and average the CU values.