Irrigation Flow Calculator

Divide your supply’s flow by one sprinkler’s flow. A spigot delivering 8 GPM (30 L/min) runs about three or four 2 GPM (8 L/min) spray heads at a time — try to run more and every head sputters. That per-zone limit, not the yard size, is what dictates the zone count.

The bucket test: time how long your supply takes to fill a 5-gallon bucket flat out, then GPM = 300 ÷ seconds (a 5-gallon bucket in 30 seconds is 10 GPM). Do it at the time of day you’ll irrigate — municipal pressure (and therefore flow) drops in the morning peak when everyone waters.

Zones = total sprinkler demand ÷ usable supply, rounded up. Sixteen heads at 2 GPM (7.5 L/min) is 32 GPM (120 L/min) of demand; on an 8 GPM (30 L/min) supply that is four zones, each running in turn off its own valve. The calculator totals it and adds a margin so zones don’t run at the ragged edge.

Typical figures: fixed spray heads 1.5–2.5 GPM (6–10 L/min), rotors 2.5–5 GPM (10–20 L/min), drip lines about 0.5–1 GPH (2–4 L/h) per emitter (a different world — hundreds of drippers fit on one zone). Check the nozzle chart for your heads at your pressure; flow rises and falls with pressure.

Pressure. Nozzle charts quote throw at a stated pressure (often 30–45 psi / 2–3 bar); friction in undersized pipe and too many heads per zone eat it, shrinking the radius and coarsening the spray. If coverage is weak, split the zone or upsize the supply pipe rather than adding heads.