Drip Irrigation Runtime Calculator
Weekly drip hours from need, heads, and flow.
What it does
Drip puts small flows at the roots over long times. The math is simple once the zone is known: weekly gallons divided by gallons per hour gives weekly hours. The hard part is honest inputs, because plant need varies with species, sun, soil, and heat.
The tool above handles the arithmetic. With 20 gal a week and ten 1 GPH emitters, zone flow is 10 GPH and runtime is 2 h a week, or 120 min. The metric mirror at 76 L with ten 3.8 LPH heads gives the same 2 h. Splitting into morning sessions helps on slopes and clay, where water needs time to soak in.
Emitter choice sets the pace. Home guides often start near 0.5 GPH on clay, 1.0 on loam, and 2.0 on sand, with tighter spacing on sand because water spreads less sideways. Maker sheets give exact flows at pressure, and pressure above about 30 psi needs a regulator or flows run high and joints fail.
This page times one zone for one week. It does not set plant need, schedule by weather, or design pipe size and filtration. Use local extension tables for need, then let the tool turn need into hours.
How to use
- Pick imperial (gal, GPH) or metric (L, LPH).
- Enter the zone water need for one week.
- Enter the count of emitters on that zone.
- Enter the flow of one emitter.
- Read hours and minutes per week, plus total zone flow.
- Split the minutes into 2 or 3 sessions to cut runoff.
Formula
- need
- Plant water need for the zone for one week, in gal or L.
- emitters
- Count of drip emitters watering that zone.
- flow
- Maker rated flow of one emitter, in GPH or LPH at working pressure.
Flow is per emitter in GPH or LPH, and water is per week in the same volume unit. At zero emitters there is no delivery; very high flows leave microirrigation and behave like sprinklers.
Worked example
Example: 20 gal a week on 10 emitters
Defaults: imperial 20 gal a week through 10 emitters at 1 GPH. Metric mirror is 76 L through 10 at 3.8 LPH.
- Inputs (imperial default): 20 gal per week, 10 emitters, 1 GPH each.
- Zone flow: 10 times 1 is 10 GPH total.
- Hours: 20 / 10 is 2 h per week.
- Minutes: 2 times 60 is 120 min per week.
- Split into two 60 min sessions on loam. Metric mirror (76 L, 10 at 3.8 LPH) gives 2 h per week and 120 min per week.
Reference table
| Zone | Flow | Time |
|---|---|---|
| 20 gal, 10 at 1 GPH | 10 GPH | 2 h (120 min) |
| 30 gal, 15 at 0.5 GPH | 7.5 GPH | 4 h (240 min) |
| 76 L, 10 at 3.8 LPH | 38 LPH | 2 h (120 min) |
| 100 L, 20 at 2 LPH | 40 LPH | 2.5 h (150 min) |
| 10 gal, 5 at 2 GPH | 10 GPH | 1 h (60 min) |
Limits
- One zone, one week. Multi zone yards need one pass per valve.
- Plant need is input, not output. Wrong need gives wrong hours.
- Rated flow at working pressure. Clogged or high pressure heads differ.
- No pipe, pump, or filter sizing. Hydraulics are separate.
Common mistakes
- Mixing GPM with GPH and missing a factor of 60.
- Counting heads on other valves as if on this zone.
- Running one long session that ponds and runs off.
- Skipping the filter and regulator, then fighting clogs.
- Watering turf and shrubs on one schedule.
Try it yourself
Quick checks. Answers sit tucked under each question.
30 gal, 15 emitters at 0.5 GPH?
Zone flow is 15 times 0.5 is 7.5 GPH. Hours are 30 / 7.5 is 4 h per week, or 240 min.
100 L, 20 emitters at 2 LPH?
Zone flow is 20 times 2 is 40 LPH. Hours are 100 / 40 is 2.5 h per week, or 150 min.
Questions
How is runtime figured?
Hours = gallons needed / (emitters times GPH). Here 20 / 10 is 2 h per week.
How do GPM and GPH relate?
GPM times 60 is GPH. A 0.25 GPM head is 15 GPH, far above drip rates.
Which emitter flow should I pick?
Clay near 0.5, loam near 1.0, sand near 2.0 GPH per emitter in many home guides. Check the maker sheet for the exact head.
Should sandy soil run more often?
Yes. Sandy soil drinks fast and holds little, so two or three shorter sessions beat one long flood.
What parts does drip need besides emitters?
Add a filter, a pressure regulator under about 30 psi, and flush caps. Most clogs come from dirt and high pressure.
Does the tool know my plants need?
No. Start from plant need or a local extension table, then use this tool for time. Guessing gallons is the main error.