| Scenario | Area | Precip rate | Efficiency | Net depth | Recommended runtime | Cycle plan |
|---|---|---|---|---|---|---|
| Loam lawn zone | 500 ft² | 1.20 in/hr | 0.75 | 0.50 in | 33.3 min | 2 × 16.7 min, soak 20 min |
| Clay bed zone | 200 ft² | 0.60 in/hr | 0.70 | 0.40 in | 57.1 min | 3 × 19.0 min, soak 25 min |
| ET interval plan | 350 ft² | 0.95 in/hr | 0.80 | 0.46 in | 36.3 min | 2 × 18.1 min, soak 15 min |
- Measure or estimate zone area and sprinkler precipitation rate.
- Select your goal: target depth or ET replacement interval.
- Choose a soil intake preset, or enter a custom intake rate.
- Enter slope, efficiency, and optional effective rainfall.
- Use auto cycle mode first, then observe runoff during cycle one.
- Export results to build a zone-by-zone watering reference.
Why precipitation rate is the anchor metric
Precipitation rate expresses how fast your sprinklers apply water across a zone. It converts a depth goal into minutes, letting you compare rotor and spray zones fairly. Measuring with catch cups reduces guesswork and reveals pressure problems, clogged nozzles, and coverage gaps that waste water. When rates differ between heads, matched precipitation is lost and dry spots appear even with long runtimes.
Balancing net depth and system efficiency
Plants respond to the water that reaches the root zone, not what leaves the nozzle. The calculator separates net depth from gross depth by dividing by application efficiency. Lower efficiency means longer runtime to compensate for wind drift, evaporation, overspray, or uneven distribution across the zone. Calibrating efficiency after repairs prevents overwatering and helps keep nutrients in the soil profile.
Using ET replacement for seasonal accuracy
ET based scheduling links irrigation to weather demand. Reference ET0 estimates atmospheric thirst, while Kc adjusts for plant type and growth stage. Multiplying ET0 by Kc and the watering interval produces a target depth that naturally increases during heat and decreases during cooler periods. Pairing ET with effective rainfall keeps schedules realistic after storms and avoids watering saturated beds.
Cycle-and-soak to control runoff on slopes
Runoff occurs when application exceeds soil intake, especially on compacted ground or sloped lawns. The cycle-and-soak logic limits each cycle to a fraction of the slope-adjusted intake rate, then adds soak time for infiltration. This approach improves uniformity and reduces puddling near hardscapes. Shorter cycles also protect seedlings by reducing surface sealing and crust formation during afternoons.
Turning results into a repeatable zone plan
After calculating, record zone notes and export the report for reference. Recheck settings after nozzle changes, repairs, or seasonal tune-ups. A consistent zone plan helps you standardize runtimes, verify smart controller recommendations, and quickly adjust when rainfall, wind, or plant stress signals a change. Audits make it easier to spot leaks, stuck valves, and drifting spray patterns before bills rise.
How do I find my precipitation rate?
Use a catch-cup test: place several cups in the zone, run sprinklers for a measured time, average the depth, then convert to depth per hour. Nozzle charts are a good starting estimate.
What efficiency value should I use?
Start with 0.70–0.80 for well-tuned systems. Use lower values if wind, overspray, or uneven coverage is common. Improve efficiency by fixing leaks, leveling heads, and matching nozzle types.
When should I choose the ET method?
Use ET when you want runtimes to follow weather demand. It works best when you have a reliable ET0 source and a reasonable Kc for your plants, especially across seasonal temperature swings.
Why does slope affect cycle length?
On slopes, water moves downhill before it soaks in. Short cycles reduce surface flow, letting infiltration catch up during soak periods. This improves uniformity and reduces runoff near sidewalks and driveways.
How often should I recalculate?
Recalculate at least seasonally, and anytime you change nozzles, pressure, or planting density. Also update after major weather shifts, overseeding, or soil amendments that alter infiltration and water-holding behavior.
Does the calculator replace local watering rules?
No. Use it to estimate minutes, then apply your local schedule restrictions and common-sense observation. If plants show stress or soil stays soggy, adjust depth, interval, or cycle settings accordingly.