Calculate total flow for drip irrigation systems.
The drip irrigation calculator totals the flow demand of a drip zone so you can check it against what your faucet, pressure regulator, and mainline tubing can actually supply. Enter the length of each drip line in feet, the emitter spacing in inches, the per-emitter flow in gallons per hour (GPH — typically 0.5, 1, or 2 GPH on inline tubing), and how many lines the zone contains. The tool returns emitters per line, flow per line, and total zone flow in both GPH and GPM — the number you compare with your supply.
Emitters per line = ⌊line length (ft) × 12 ÷ emitter spacing (in)⌋ — the floor because a partial emitter cannot exist. Flow per line (GPH) = emitters × per-emitter GPH. Total flow (GPH) = lines × flow per line, and GPM = GPH ÷ 60. If the total exceeds the supply, pressure drops at the far ends and the last emitters under-deliver; the standard fix is splitting the zone or stepping down to lower-flow emitters.
Four 50 ft lines with 12 inch spacing and 0.5 GPH emitters: 50 emitters per line, 25 GPH per line, 100 GPH total ≈ 1.67 GPM. A typical outdoor spigot supplying 4–6 GPM handles this zone comfortably.
Six 25 ft lines at 18 inch spacing: ⌊25 × 12 ÷ 18⌋ = 16 emitters per line, 16 GPH per line, 96 GPH ≈ 1.6 GPM total. Note the floor function at work — 16.67 rounds down, not up.
One 100 ft line, 24 inch spacing, 2 GPH emitters: 50 emitters, 100 GPH ≈ 1.67 GPM. Long single runs like this are also where tubing flow limits matter — check the maximum run length for your tubing diameter.
A 25 ft line with 18 inch spacing works out to 16.67 positions, but you can only install whole emitters — so the tool floors to 16. Rounding up would overstate the zone's real flow demand.
0.5 GPH suits closely spaced vegetables and slow-draining clay; 1 GPH is the general-purpose default; 2 GPH fits trees, shrubs, and sandy soil that drains quickly. Mixing rates on one line makes watering uneven — keep each line uniform.
Time how long your spigot takes to fill a 5-gallon bucket: 60 seconds means 5 GPM. Keep the zone's GPM total below about 75% of that to leave headroom for filter and pressure-regulator losses.