To apply a target depth of water, a sprinkler zone runs for a time set by its precipitation rate (inches per hour). Target inches ÷ precip rate × 60 gives the runtime in minutes.
The example
0.5 inch, 1.5 in/hr zone.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 0.5 / 1.5 × 60 | — |
| 3 | Runtime | → 20 min |
The formula
The formula:
How it works
How it works:
- The precipitation rate (in/hr) is how fast that zone applies water — measured with catch cups.
- Target inches ÷ precip rate gives hours; × 60 for minutes.
- Split into cycle/soak intervals on slopes to prevent runoff.
- Sum runtimes across zones for the total watering window.
Every zone has its own precipitation rate — one runtime does not fit all. Spray heads apply water far faster (often 1.5–2 in/hr) than rotors (~0.5 in/hr), so a spray zone needs a fraction of a rotor zone’s runtime for the same depth. Measure each zone with catch cups, compute its own runtime, and on slopes break it into cycle-and-soak intervals so water absorbs instead of running off.
Try it: interactive demo
Target depth (inches) and precip rate (in/hr).
Variations
Cycle/soak
Split runtime:
Total window
Sum zones:
Precip from catch cups
Measured rate:
Pitfalls & errors
Per zone. Each zone’s precip rate differs — spray vs rotor.
×60 for minutes. Depth÷rate is hours; convert to minutes.
Cycle and soak. Split runtime on slopes to avoid runoff.
Practice workbook
Frequently asked questions
How do I calculate irrigation zone runtime in Excel?
How do I find a zone's precipitation rate?
Why split into cycle and soak?
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