What the animation shows
The animation and the step-by-step video above use your numbers. Here is the same walkthrough written out for the default example.
What you enter
- Bucket size: 5 gal.
- Seconds to fill: 30 s.
- Usable share of available flow: 75 %.
- Sprinkler heads: 12.
- Flow per head: 1.5 gpm. From the nozzle chart at your pressure.
- Area watered by these heads: 2000 sq ft.
- Water to apply: 0.5 in.
What happens, step by step
- Timing how fast a 5 gal bucket fills measures your spigot's flow.
- Use 75% of it: 5 heads at 1.5 gpm fit in one zone.
- 12 heads need 3 zones, watering one zone at a time.
- Heads put down 0.87 in/h, so 0.5 in takes 35 min per zone.
The answer: zones needed is 3 zones.
How it’s calculated
- Available gpm = bucket gallons ÷ seconds × 60
- Heads per zone = (available × usable %) ÷ head flow, rounded down
- Precipitation rate (in/h) = 96.25 × total gpm ÷ area
- Run time = target depth ÷ precipitation rate
Worked example
5 gal bucket fills in 30 s; 12 heads at 1.5 gpm covering 2,000 sq ft; apply ½ in.
Inputs
- Bucket size
- 5 gal
- Seconds to fill
- 30 s
- Usable share of available flow
- 75 %
- Sprinkler heads
- 12
- Flow per head
- 1.5 gpm
- Area watered by these heads
- 2000 sq ft
- Water to apply
- 0.5 in
Results
- Zones needed
- 3 zones
- Available flow
- 10 gpm
- Total head flow
- 18 gpm
- Maximum heads per zone
- 5
- Precipitation rate
- 0.87 in/h
- Run time per zone for target
- 35 min
Assumptions and limits
- Heads are spaced head-to-head with matched precipitation.
- Pressure loss in the pipe is not modelled; a pressure gauge test is recommended.
Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.
Questions
How many sprinkler heads per zone?
Divide the usable flow by each head’s gpm. With 10 gpm available and 75% usable, 1.5 gpm heads allow 5 per zone.
How long should I run sprinklers?
Divide the water depth you want by the precipitation rate. Most lawns need about 1 in per week, split into a few sessions.