Upkeep PlanTimed by soil temperature

Irrigation audit: the tuna can test and how to use the results

The minutes on the controller are a guess until you measure what each zone puts down. Catch cans turn that guess into inches per hour — then into a run time for the depth you want.

Skip the arithmetic

Enter test minutes and average can depth in the sprinkler run time calculator. This page is the field method and the citations behind the formula.

Set up the catch-can test

Tuna can test: straight-sided cans scattered in one sprinkler zone, run the zone, measure average depth, calculate run time for a target depth Top-down view of a lawn zone. A rotor sprinkler sits near the center. Five tuna or coffee cans are placed within the spray pattern. One can is shown in cross section with water depth measured by a ruler. Run one zone at a time — rates differ by zone and by head type.00.25"0.5"0.75"1"MeasureOne zone · scatter 5–10 cans · run · average the depths
One zone at a time. Straight-sided cans (tuna, coffee, rain gauges) catch the same spray the turf sees — UF/IFAS ENH61 and AE220.
  • Same zone only — rotor and spray heads apply water at different rates
  • Average every can — dry spots and overlap both show up in the spread
  • Repeat per zone — set run times separately on the controller
  1. One zone. Shut off every other valve. Rotor and spray zones need separate tests.
  2. Cans. UF/IFAS ENH61: 5–10 cans, about 3–6 inches across, same size. AE220: at least six per zone, rims above the turf and level, at least one foot from heads.
  3. Scatter. Place cans at random across the zone (ENH61). Minnesota Extension uses a grid — sprays every 5–8 ft, rotors every 10–20 ft — if you want a denser sample.
  4. Run a fixed time. ENH61 and UC IPM disease guidance often use 15 minutes. Minnesota prefers 30–60 minutes for a cleaner average. Write the minutes down.
  5. Measure. Ruler in each can; ENH61 says nearest ⅛ inch is fine. Average = sum ÷ number of cans.

Turn average depth into run time

From UF/IFAS AE220:

AR (in/hr) = Depth × 60 ÷ Time
Time (min) = 60 × Target depth ÷ AR

Shortcut when the test ran exactly 15 minutes (ENH61): average depth × 4 = inches per hour. Example: ¼ inch in 15 minutes → 1 in/hr → 30 minutes for a ½-inch target.

Target depthat ½ in/hrat 1 in/hrat 1½ in/hr
½ in60 min30 min20 min
¾ in90 min45 min30 min
1 in120 min60 min40 min

Minutes adapted from UF/IFAS ENH61 Table 1 and AE220’s Time = 60 × Depth / AR. Florida guidance also notes many events should stay around ½–¾ inch so runoff does not waste the rest.

If the cans disagree

Minnesota Extension: distribution uniformity from the lowest quarter of cans divided by the overall average — under about 60%, fix the system before you trust the timer. Adjust heads, pressure and overlap; then retest. A perfect average from a broken zone still leaves dry spots.

Questions people actually ask

What is an irrigation audit for a home lawn?

You measure what one zone actually puts down with catch cans, average the depth, convert to inches per hour, then set the controller run time for the depth you want. UF/IFAS and Minnesota Extension both publish this catch-can method.

How do I calculate run time from the can test?

UF/IFAS AE220: application rate AR = Depth × 60 ÷ Time (inches and minutes). Then Time for a target depth = 60 × Depth ÷ AR. Example: 0.25 inch in 15 minutes is 1 inch per hour — a 0.5-inch target needs 30 minutes.

How many cans and how long should I run?

UF/IFAS ENH61: 5–10 straight-sided cans, 15-minute test, average to the nearest ⅛ inch. AE220 asks for at least six cans per zone. Minnesota Extension prefers a denser grid and 30–60 minutes for accuracy — longer tests reduce measurement error.

What if some cans are full and others are empty?

That is a uniformity problem, not a timer problem. Minnesota Extension’s low-quarter distribution uniformity under about 60% means fix heads, pressure, or spacing before you trust a single run time. UF/IFAS: large differences mean inspect the system.

Do I audit every zone?

Yes. Spray and rotor heads apply water at different rates. Minnesota Extension: set run times zone by zone on the controller.

Sources