How many emitters and how much flow?
A drip system is sized by flow. Count the emitters, multiply by each emitter's flow in gallons per hour (GPH), and check the total against what your tubing and water supply can deliver. If it's too much, split the system into zones that run one at a time.
Emitters = run length (ft) × 12 ÷ emitter spacing (in)
Total GPH = emitters × GPH per emitter · GPM = GPH ÷ 60
One 100 ft run with emitters every 12 inches has 100 emitters. At 1 GPH each that's 100 GPH, or 1.67 GPM, which fits in one zone. Two 150 ft runs at the same spacing are 300 emitters and 300 GPH. That's over a 240 GPH limit, so the calculator splits it into 2 zones.
Emitter flow and spacing
| Emitter flow | Typical use | Common spacing |
|---|---|---|
| 0.5 GPH | Clay soil, containers, small plants | 12–18 in in clay |
| 1 GPH | Most beds and vegetable rows | 12 in in loam, 12–18 in in clay |
| 2 GPH | Sandy soil, shrubs, trees | 12 in or closer in sand |
Water spreads sideways farther in clay than in sand, so sandy soil typically needs closer spacing or higher-flow emitters. For shrubs and trees, use one or more emitters per plant instead of a fixed spacing, and enter the total as a separate run.
Drip irrigation for a bed in square feet
To cover a whole bed, lay parallel rows of tubing. Divide the bed's area by the row spacing in feet to get the tubing length. A 10 × 20 ft bed is 200 sq ft. With rows 18 inches apart, that's 200 ÷ 1.5 = 133 ft of tubing. With emitters every 12 inches at 1 GPH, it's 133 emitters and 133 GPH.
Rows 12–18 inches apart suit most beds. Drip tape for vegetable rows works the same way: enter the length of each row as a run.
Zones and the 240 GPH figure
Two things cap a zone: the tubing and the water supply. Tubing makers publish a maximum flow and run length for each size. For 1/2 in tubing, 240 GPH and about 200 ft per run from one feed point are common figures, but check the spec for the tubing you buy and enter it. Your supply is the other limit. Time how long it takes to fill a 5 gallon bucket at the tap, then work out gallons per hour and keep each zone below it.
Parts you'll need
Each zone needs a head assembly at the tap or valve: a backflow preventer, a filter and a pressure regulator, since most drip parts are rated for far lower pressure than a house supply. Each run needs a connector at the feed end and an end closure. Stakes hold the tubing down, typically every 3–5 ft. If several zones share one valve manifold, they can often share one backflow preventer and filter; lower the zone head kit price to match.
Pricing a drip irrigation job
Irrigation contractors usually price drip by the zone, built from parts at cost plus markup and labor for laying tubing, installing emitters and plumbing the head assembly. Connecting to a valve manifold or controller adds time, and local code may require a specific backflow device. Set your hours in contractor mode, then send it as a landscaping estimate.
Questions
How many emitters can I put on a 1/2 inch drip line?
Divide the tubing's maximum flow by the emitter flow. At a 240 GPH limit, that's 240 emitters at 1 GPH or 120 at 2 GPH. Check the limit for your tubing.
How do I convert GPH to GPM?
Divide by 60. 120 GPH is 2 GPM.
How far apart should drip emitters be?
Typically 12 inches in loam, 12–18 inches in clay, and 12 inches or closer in sand. Shrubs and trees usually get one or more emitters per plant.
How long can a 1/2 inch drip line be?
Many manufacturers list about 200 ft per run from a single feed point. Longer runs lose pressure at the far end, so feed them from the middle or split them.