Calculate sprinkler runtime
Enter your catch-can depth, test minutes, and target inches.
Catch cans beat controller guesses
Sprinkler heads, pressure, spacing, wind, slope, and nozzle wear change how much water actually reaches the lawn. UMN Extension recommends placing catch cans through a zone, running the zone, measuring the collected depth, then calculating precipitation rate and runtime from that measured output.
The math
Precipitation rate is average catch depth divided by test minutes, multiplied by 60. Runtime is target inches divided by precipitation rate, multiplied by 60. Example: 0.25 inch in 15 minutes equals 1.0 inch per hour, so 0.5 inch takes about 30 minutes.
Use the result carefully
- Test each zone separately.
- Use several straight-sided catch cans, not one cup.
- Split runtime into cycle-and-soak runs if water starts to run off.
- Subtract meaningful rain and check soil moisture before watering again.