Sprinkler Precipitation Rate Chart

Typical precipitation rates by sprinkler type

A sprinkler's precipitation rate is how fast it applies water, measured as a depth per hour, the same way rain is measured. It's the number you need to set run times, and it varies a lot between types of sprinkler.

The gap is large. At Colorado State's typical 1½ inches per hour, a spray zone puts down a quarter inch in about 10 minutes. A rotor zone at ½ inch per hour needs 30 minutes for the same quarter inch. That's why the two need very different run times, and why they shouldn't share a zone.

Rotary nozzles fit on spray head bodies but apply water at rotor-like rates. Swapping them in is one of the common ways to lower a zone's rate, but it also means the zone's run times must go up.

Low rates matter most on slow-draining soil. Colorado State notes that the slower rate of rotors can be an advantage on clay or compacted soils, where water soaks in slowly. To compare your rate with your soil, see the soil infiltration rate chart.

How long it takes to apply water at each rate

Run time is the depth you want divided by the precipitation rate. This table shows common combinations, rounded to the nearest minute.

If water starts to run off before the time is up, split the run into shorter cycles. The cycle and soak calculator works out the split. For minutes per session from your sprinkler type and soil, use the how long to water lawn calculator.

Precipitation rate chart by nozzle flow and spacing

If you know the flow of your nozzles and how far apart your heads are, these charts give the design precipitation rate directly. Each value is calculated from the standard formula, for full-circle heads laid out in a square pattern with head-to-head coverage. For part-circle heads, use the flow of the full-circle equivalent, as explained under matched precipitation.

Spray heads (US units)

Rotors (US units)

Spray heads (metric)

Rotors (metric)

Nozzle flow is on the manufacturer's nozzle chart for your operating pressure. For layouts that aren't in these charts, the sprinkler precipitation rate calculator handles any flow, spacing and pattern.

Sprinkler precipitation rate formulas

The constant 96.25 converts gallons per minute over square feet into inches per hour. A gallon is 231 cubic inches and a square foot is 144 square inches, so 231 ÷ 144 × 60 minutes = 96.25.

Worked examples

1. Spray heads, square spacing: full-circle nozzles flowing 2.6 GPM at 15 ft × 15 ft. 96.25 × 2.6 ÷ 225 = 1.11 in/hr.
2. Same heads, triangular spacing: 96.25 × 2.6 ÷ (225 × 0.866) = 1.28 in/hr. The triangle packs heads closer together, so the rate rises.
3. Metric: full-circle nozzles flowing 10 L/min at 4 m × 4 m. 60 × 10 ÷ 16 = 37.5 mm/hr.

Matched precipitation: part-circle heads

A half-circle head covers half the area of a full-circle head, so it needs half the flow to apply water at the same rate. A quarter-circle head needs a quarter. When flow follows the arc like this, the heads have matched precipitation, and the whole zone waters evenly.

Hunter Industries works through the numbers for a 30 ft radius: a full circle flowing 4 GPM, a half circle flowing 2 GPM and a quarter circle flowing 1 GPM all apply about 0.136 in/hr over their own coverage. Put the same 4 GPM nozzle on all three instead, and the rates become 0.136, 0.273 and 0.545 in/hr. The corners then get four times as much water as the middle of the lawn.

This is also why spray heads and rotors shouldn't share a zone: they apply water at very different rates. Colorado State University Extension advises not mixing sprinkler types in a zone. The exception is equipment made to match, such as Rain Bird's Rotary Nozzles, which the manufacturer rates as matched with its 5000 series MPR rotor nozzles. To check the heads in one of your zones, use the matched precipitation calculator.

Chart values vs your actual system

Every figure on this page is a design value: the rate a sprinkler should apply with nominal flow and ideal spacing. Real zones often differ, for several reasons:

• Pressure. Nozzle flow changes with pressure, so a zone running above or below the nozzle chart's pressure applies a different rate.
• Spacing. Heads placed farther apart than head-to-head lower the rate and leave dry areas between heads.
• Mixed or worn nozzles. A replacement nozzle from a different series, or a worn one, changes the flow of that head.
• Wind and slope. Wind distorts the pattern, and water runs downhill before it soaks in.

The only way to know your real rate is to measure it. Set out straight-sided cans across a zone, run it for a set time and measure the water collected. The catch-can test calculator turns the readings into a precipitation rate. Use that measured rate for your run times rather than a chart value.

Frequently asked questions

Who built and checked this chart

Daniel Reeves, PE, CID

Irrigation Design Engineer & Water-Efficiency Specialist

Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile

How this page was checked

• Type ranges checked against Colorado State University Extension and each manufacturer's published data.
• Every chart value calculated from the standard formulas, and the worked examples verified by hand.
• Matched precipitation figures checked against Hunter's published example.

Last reviewed September 25, 2026. Methodology, editorial policy, report an error.

Sources

• Colorado State University Extension, Colorado Master Gardener program. Sprinkler Types Used for Lawn Irrigation.
• Hunter Industries. Residential Rotors: Matched Precipitation Rates.
• Hunter Industries. MP Rotator Design Guide.
• Rain Bird. Rotary Nozzles Tech Spec.
• Toro. Precision Series Rotating Nozzles.