Irrigation Run Time Calculator
Run time is the product of what you want to apply (target inches) and how fast your system delivers it (precipitation rate). This converts both into minutes per watering.
Formula: run time (min) = (target water depth ÷ precipitation rate) × 60. Weekly water = per-watering inches × days. Reference volume: 1 inch over 1,000 sq ft = 623 gallons; 1 inch over 1 acre = 27,154 gallons. Use: set your target from evapotranspiration (ET) minus rainfall for your area (NOAA, state CIMIS/AgriMet), then fill to match your system's measured precipitation rate (catch-can test or zone GPM).
FAQ
How do I find my sprinkler precipitation rate?
Use the catch-can method: place straight-sided cans in a zone, run it 10 minutes, average the water depth, and multiply by 6 for inches per hour. Or compute it from zone GPM with a sprinkler-rate calculator.
How much should I water my lawn?
Many lawns need about 1 inch of water per week during the growing season, minus rainfall. Divide it across 2-3 waterings; water deeply and less often to encourage deep roots.
Why is my run time long?
Low precipitation rate (drip, low-pressure heads) or a high target depth both lengthen run time. If a single cycle exceeds 60 minutes, split it into two to prevent runoff, especially on slopes or compacted soil.
Figures are editable example defaults for planning, not guarantees. Water needs vary by crop, soil, weather, season, and local climate — check ET data (NOAA, your state CIMIS/AgriMet network) and verify with your local extension service or agronomist.