Drip Emitter Calculator
Size a drip zone from the plants up: how many emitters your plants need, how much flow the valve must supply, and how long to run it for the weekly water target.
Inputs
Result
Planning estimate - not a substitute for a pressure-tested engineering design.
Formula
Total emitters = plants × emitters per plant. Zone flow = emitters × emitter GPH. Run time per week (min) = gallons per plant ÷ (emitters per plant × GPH) × 60; per session = weekly ÷ watering days.
Example
40 shrubs, two 1 GPH emitters each, 4 gal/week per plant, 2 watering days: 80 emitters, zone flow 80 GPH, run time 4 ÷ 2 × 60 = 120 min/week → 60 minutes per session, ~160 gallons a week.
Assumptions
- Pressure-compensating emitters hold flow constant along the line.
- Emitters wet overlapping root zones - spread them around the canopy edge, not the stem.
- Keep each valve's total GPH in the 100-300 range for easy scheduling.
Limitations
This tool is a planning aid for DIY design and pre-design work. It does not replace an on-site pressure and flow test, a catch-cup uniformity test, or local code and backflow requirements. For steep slopes, long pipe runs, large elevation changes or commercial-scale systems, have a qualified irrigation designer verify the plan before installation.
What This Means
Emitter count is a root-zone decision, not a flow decision: more emitters spread water wider, they do not water faster (total GPH rises). Match the zone flow to your valve capacity, then schedule by minutes.
Next Step
Check how much water this zone uses with the Water Use Calculator, or budget the whole landscape with the Water Budget Calculator.
Sources
Frequently Asked Questions
How many emitters do I need per plant?
Enough to wet the whole root zone: 1 for vegetables and annuals, 2-3 for shrubs, 3-6 for trees spread at the canopy edge. Wet width matters more than flow.
Can I mix 0.5 and 2 GPH emitters on one line?
Avoid it on non-compensating lines - flow follows the path of least resistance. With pressure-compensating emitters it works, but scheduling is simpler when a zone uses one emitter type.