A drip system only works if your tap can supply enough water to run all of its emitters at once. If a zone asks for more than the tap can give, the far end of the line gets little or nothing. This irrigation zone flow calculator checks it. Enter the plants on the zone, the emitters per plant and the flow of each emitter, plus the result of a simple bucket test at your tap, and it tells you the total flow needed, how many zones you require and the most emitters one zone can carry.
How to do the bucket test
- Open the tap fully with the hose attached, with no sprinkler or timer on it.
- Time how long it takes to fill a 5-gallon bucket, in seconds.
- Enter that number in the calculator. Faster fill means more flow.
How to use the irrigation zone flow calculator
- Enter the plants and the number of emitters on each.
- Choose the flow of each emitter. Common drip emitters are 0.5, 1, 2 or 4 gallons per hour; the number is on the package.
- Enter your bucket time and the spare capacity you want to keep in reserve.
- Read the results. You get total flow, how much your tap supplies, the zones needed and the most emitters per zone.
How the calculation works
Total flow in gallons per hour is the plants times the emitters per plant times the flow of each emitter. Dividing by sixty gives gallons per minute. Your tap’s flow is five gallons times sixty seconds divided by the seconds the bucket took to fill. The calculator keeps a share in reserve, because running a system at the very limit of your supply can leave pressure too low, then divides the flow you need by the flow you can use to get the number of zones.
Splitting a system into zones
| Situation | What to do |
|---|---|
| Flow needed is below your usable supply | One zone is enough |
| Flow needed is above it | Split the plants into two or more zones and run them one at a time |
| Beds are in different sun or soil | Zone by need, since they may want different run times |
Tips for a drip system that works
- Use a filter and pressure regulator. Drip tubing is made for low pressure, often around 25 psi, so check the maker’s rating.
- Follow tubing length limits. Long runs lose pressure, and flow drops toward the end.
- Flush the lines at the start of the season and the end.
- Time the run to deliver the water your plants need. The garden water budget planner and the drip irrigation calculator help.
- Consider soaker hose for simple beds. See the soaker hose length calculator.
Limits of this tool
The bucket test measures flow at the tap with nothing attached, and pressure and elevation change what reaches the emitters. Treat the result as a design check and follow the instructions for the drip parts you buy. Local rules may also restrict when you can irrigate.
Frequently asked questions
How do I know if my tap can run my drip system?
Do the bucket test, then compare your tap’s gallons per minute with the flow your emitters need.
What is a gallon per hour emitter?
An emitter that releases one gallon of water in an hour. Common sizes are half a gallon to four gallons per hour.
Why keep spare capacity?
Running at the full tap flow leaves no margin for lower pressure, which makes emitters deliver unevenly.
How many emitters can one zone run?
It depends on your tap flow and emitter size. The calculator shows the maximum for your numbers.
Do I need a pressure regulator?
Usually yes. Most drip parts are made for low pressure and can burst or leak at household pressure.