Drip Line Flow Calculator
Size a drip zone by flow, not spray: add up the total flow in GPH and GPM from the number of emitters and each emitter’s rate, and keep your run of drip tubing on record.
Calculator
50 emitters at 1.0 GPH each draw about 50.0 GPH (0.83 GPM) over 200 ft of tubing. Keep each zone under the tubing's max flow and length — check the manufacturer's limits.
Drip irrigation delivers water slowly and precisely to roots — ideal for beds, borders, hedges, containers and vegetable rows — with almost no evaporation or overspray. But it’s sized completely differently from sprinklers: you don’t think in spray radius, you think in summed emitter flow. Too many emitters on one line, or too long a run, and the far end starves.
This tool adds up the flow of every emitter on a zone and converts it to GPM so you can check it against your available supply, and it keeps your tubing length on record against the manufacturer’s maximum run. It’s pure arithmetic on the numbers printed on your parts — no live data, nothing to maintain.
Formula
Drip zones are governed by total flow. Add up every emitter’s rate to get the zone’s demand, then convert to GPM to compare against your supply:
total_gph = emitters × emitter_gph
total_gpm = total_gph ÷ 60Unlike sprinklers, drip is rated in gallons per hour because the flows are tiny and deliberate. The tubing length matters for a different reason: each size of poly tubing has a maximum flow and a maximum run before friction starves the far end — so you keep both the summed flow and the run within the manufacturer’s limits.
Worked example
A raised-bed zone with 50 emitters at 1 GPH each, on 200 ft of 1/2″ tubing:
- Total flow = 50 × 1 = 50 GPH
- In GPM = 50 ÷ 60 = 0.83 GPM
That’s a gentle 0.83 GPM — well within a typical 1/2″ line’s capacity, and a fraction of a sprinkler zone’s draw, which is why drip can run longer and even overlap with other watering. Check that 200 ft is inside your tubing’s maximum run so the last emitter still drips at rate.
Emitter & tubing figures
Common emitter and tubing figures (labeled planning typicals — always confirm on the part and the manufacturer’s chart):
- Emitter rates: 0.5, 1 and 2 GPH are the usual sizes; smaller emitters suit slow-draining soil and closer spacing.
- 1/2″ poly tubing: commonly rated to roughly 200–240 GPH and a few hundred feet of run — check your brand.
- 1/4″ micro tubing: for short branches only; keep runs very short to avoid pressure loss.
- Pressure regulation: most drip runs at low pressure (often ~25–30 psi); pair the zone with a regulator and a filter.
If a zone’s summed flow or run exceeds the tubing’s limit, split it into two zones or step up a tubing size. To set run times for a bed, translate the plant water need into gallons and divide by the zone’s GPH.
Reference table
Total flow at your emitter rate of 1.0 GPH each:
| Emitters | Total GPH | Total GPM |
|---|---|---|
| 25 emitters | 25.0 GPH | 0.42 GPM |
| 50 emitters | 50.0 GPH | 0.83 GPM |
| 100 emitters | 100.0 GPH | 1.67 GPM |
| 150 emitters | 150.0 GPH | 2.50 GPM |
Keep summed flow and run length within the tubing’s rated limits.
Frequently asked questions
Why is drip rated in GPH instead of GPM?
Because the flows are deliberately tiny — a single emitter might release half a gallon over a whole hour. Gallons per hour keeps the numbers readable. To compare a drip zone against your household supply, divide the summed GPH by 60 to get GPM.
How many emitters can one line handle?
As many as fit under the tubing’s maximum flow and run. Add up every emitter’s GPH; if the total approaches the tubing’s rating, or the run is longer than the manufacturer allows, split the zone or step up a tubing size so the far emitters still drip at rate.
What emitter size should I use?
Match it to soil and spacing. 0.5 GPH suits slow-draining clay and close spacing; 1 GPH is a good all-round choice; 2 GPH suits fast-draining sandy soil or thirstier plants. The rate is printed on the emitter.
Does the tubing length change the flow?
Not the summed demand, but it does limit delivery: friction along a long run drops pressure so the last emitters underperform. Stay within the tubing’s rated maximum length, and use a pressure regulator so the whole run sees consistent low pressure.
How long should I run a drip zone?
Long enough to deliver the plants’ water need. Estimate the gallons a bed needs, then divide by the zone’s total GPH to get hours. Because drip loses little to evaporation, it typically runs longer and less often than spray.