How long should your drip system run?

What the run time means

A drip system is a slow, measured rain: each emitter drips a fixed number of gallons an hour, and the area it serves is fixed by how far apart the emitters and lines are. Divide the water a crop needs by the speed of the system and you have the hours to run it. The calculator does that in two forms. For beds with drip tape it works from the spacing and the bed width; for shrubs, trees and containers it works from the ground each plant waters.

The formulas

For tape, the University of Arkansas Extension gives the rate in inches per hour as the emitter flow in gallons per hour times 231, divided by the emitter spacing in inches times the bed width in inches. The 231 is the number of cubic inches in a US gallon. Hours per week are the weekly depth divided by that rate. Flow of a line is the emitter flow times the number of emitters on it, and flow per 100 feet is the emitter flow times the emitters in 100 feet. For single plants, the water per week is the area in square feet times the depth in inches times 0.62 (144 square inches per square foot divided by 231); that factor is our own derivation. Divide those gallons by the combined flow of the plant's emitters to get hours.

The zone check uses the 75% rule from UC Cooperative Extension: measure the faucet or pump output with a bucket and use at most three quarters of it, counting every emitter, tube and fitting on the zone.

Worked example

Take the University of Arkansas example: drip tape with 0.3 gph emitters every 12 inches in a 24-inch bed, 100 feet long. The rate is 0.3 × 231 ÷ (12 × 24) = 0.24 inch an hour, so 1 inch takes 4.2 hours, about 249 minutes. The tape has 100 emitters and runs 30 gph, which is 0.5 gpm per 100 feet. Doubling the emitter to 0.6 gph halves the time to 2.1 hours. Check against the Southeastern US Vegetable Crop Handbook table the guide reproduces: a tape that flows 11.4 gph per 100 feet at a 4-foot row spacing needs 21.9 hours for an inch, and this calculator gives 21.9.

Now the zone. A 2-gallon bucket fills in 30 seconds: that is 240 gph from the tap, and 75% of it is 180 gph. One 100-foot tape uses 30 gph, so 6 tapes can run together and 8 tapes need 2 zones. For ten shrubs with 9 square feet each and two 1 gph emitters apiece, the same supply runs 90 plants at a time, each needing 5.6 gallons a week, or 2.8 hours.

Limits of this method

• The inch is a target, not a law. Arkansas Extension notes that seedlings need less, fruiting tomatoes more, and a warm high tunnel more again. Treat the answer as the start of a schedule and adjust with a soil moisture sensor.
• Soil sets the cycle length. Clay takes water slowly but holds it; sand does the reverse. Arkansas pairs clay with lower flows and fewer cycles. If a line applies water faster than the soil can take it, split the weekly time into more, shorter waterings; the optional intake field warns you.
• Rated flow is not always real flow. Low pressure, long runs and clogged emitters cut output. UC suggests keeping a ½-inch mainline to about 200 feet per zone, and shorter where pressure is under roughly 20 to 25 psi.
• Check your units. Arkansas warns that sources mix gallons per hour, gallons per minute, hours and minutes; this page shows gph and gpm side by side to help.

How long should I run drip irrigation?

Long enough to deliver the depth of water the plants need, which for most fruit and vegetable crops is about 1 to 2 inches a week (University of Arkansas Extension). The run time is that depth divided by how fast the line applies water. A tape with 0.3 gph emitters every 12 inches in a 24-inch bed applies 0.24 inch an hour, so 1 inch takes 4.2 hours, or about 249 minutes. Split over 5 waterings that is 50 minutes each.

How many gallons per week does one plant need?

One inch of water over one square foot is 0.62 gallon (144 square inches divided by the 231 cubic inches in a gallon). A shrub or vegetable that has 9 square feet to itself therefore needs 5.6 gallons for 1 inch in a week. Through two 1 gph emitters that is 2.8 hours of running. The number to use for the area is the ground the roots actually draw from, such as a canopy footprint or a bed share, not the size of the whole yard.

How many emitters can one zone run?

Measure your supply with the bucket test: run the faucet wide open and time how long a known bucket takes to fill. A 2-gallon bucket that fills in 30 seconds means 240 gallons an hour. UC Cooperative Extension (Sonoma County Master Gardeners) treats 75% of that as the most a zone can use, here 180 gph, and says to add up every emitter and component on the zone. With the 100-foot tape above (30 gph per line) that is 6 lines at a time, so 8 lines need 2 zones.

What emitter flow rate should I pick?

Common point-source emitters are 1/2, 1 or 2 gallons per hour, and emitter line comes with emitters every 6, 12, 18 or 24 inches (UC ANR). Match the flow to the soil: clay absorbs water slowly and holds a lot of it, so the Arkansas guide pairs it with lower flow rates and less frequent cycles, while sand takes water fast but holds little. UC's rule of thumb for spacing is about 6 inches apart in sand, 12 in loam and 18 in clay. If puddles form around each emitter or water runs off the bed, the flow is too high for the soil.

Is 1 inch of water per week always right?

No, it is a starting point. The Arkansas guide says small seedlings and new transplants may need less than a full inch, a mature fruiting tomato nearer two inches, cool cloudy weather less, and a warm high tunnel more. Rain counts toward the total. The Arkansas guide suggests a reliable soil moisture sensor to dial in when and how often to irrigate.

How many gallons is an acre-inch?

27,154 US gallons: an acre is 43,560 square feet, one inch is 1/12 foot, and a cubic foot is 7.48 gallons. It is handy for field-scale checks: a 1,000-gallon tank holds 0.04 of an acre-inch, enough for 1 inch over about 1,604 square feet.

Sources: University of Arkansas System Division of Agriculture, Cooperative Extension Service, FSA6174, “Drip Irrigation Fundamentals: The Math Behind the Drip” (T. Ernst, K. Barney, A. McWhirt, L. Herrera, L. Carr, 2026), including the table from the 2026 Southeastern US Vegetable Crop Handbook; University of California Agriculture and Natural Resources, “Drip Irrigation — Intermediate” (Sonoma County Master Gardeners, 2015). Water for the lawn: lawn watering calculator; beds and soil: raised bed soil calculator, soil texture calculator; collecting rain: rainwater harvesting calculator.