Sprinkler Zone Calculator

A sprinkler zone can only run as many heads at once as the water supply can feed. Every head has a rated demand in gallons per minute, and your home has a finite supply flow at working pressure. Divide the available flow by the per-head demand and round down — you cannot run a partial head — and that whole number is the most heads one valve can drive without pressure sagging across the lawn.

Once you know heads per zone, the second answer follows: divide the total number of heads the yard needs by the heads-per-zone capacity and round up. That gives the number of zones, and therefore the number of valves and the length of the watering cycle, since zones run one after another.

The critical input is your available supply flow. Measure it by timing how long a `5 gal` bucket takes to fill from an outside spigot with everything else off: `5` gallons in `30` seconds is `10 GPM`. Undersizing a zone by guessing high on supply is the most common reason a new system throws weak, misting heads at the far end.