How many sprinkler zones do I need?

Why a sprinkler system is split into zones

You cannot run every sprinkler on the lawn at once. Each head needs a certain flow to throw its full radius at the right pressure, and a garden tap or a household water meter only delivers so much. Turn on too many heads together and the pressure drops: the sprays fall short, the heads at the end of the line barely pop up and the lawn gets dry rings.

So the heads are split into zones. Each zone has its own valve, and the controller opens one valve at a time. Zones run one after another, so your supply only has to keep up with one zone — the busiest one — never with the whole lawn. That is also why the total flow of all heads, which the calculator shows at the bottom, is not the number to compare with your tap.

What limits a zone

Two things cap how much one zone may draw, and the calculator applies whichever is lower:

1. Your water supply. If you measured it, a zone is designed to use at most 75% of that flow. The margin is there because the house may be drawing water at the same time (a shower, a washing machine) and to spare the meter; 75% of the safe flow is the figure Rain Bird recommends for irrigation on a water meter.
2. The pipe. Topoform designs with 32 mm poly pipe and 1-inch valves. Its knowledge base gives that pipe a maximum of 14.1 GPM (53 L/min) and recommends designing zones under 11.4 GPM (43 L/min). With a strong supply, the pipe is the limit; the calculator says which one applied.

How the calculator groups the heads

Enter the heads you plan to use as rows: nozzle model, arc and how many. Each head's flow comes from Hunter's published figures in Topoform's catalog, rated at 2.8 bar (41 psi). An MP2000 full circle, for example, uses 1.47 GPM (5.6 L/min), a half circle half of that and a quarter circle a quarter — MP Rotators are matched-precipitation nozzles.

The calculator then fills zones starting with the thirstiest heads, and adds each head to the first zone that still stays within the limit; when no zone has room, it opens a new one. The check for "does it still fit" is the same per-zone check the Topoform app runs on every zone of a design, so a grouping the calculator returns passes in the app as well.

Treat the zone count as a minimum. The calculator only knows the flows, not where the heads stand, so it packs them as tightly as the flow allows. On a real yard the app's Auto-design also keeps every zone a connected group of neighbouring heads, so that pipe runs stay short — and that can take one or two more zones than the flow alone would need.

The result shows:

• The minimum number of zones for all the heads.
• What goes in each zone and its total flow.
• The limit per zone and whether your supply or the pipe set it.
• Max per zone for each head type on its own — useful when you are still deciding how many heads to buy.

Mixing heads in one zone

MP Rotator arcs can share a zone freely: a full circle, a half and a quarter all put down water at the same rate, so a zone of mixed arcs still waters evenly. The rule that does matter is not to mix different kinds of heads in one zone — rotary nozzles such as MP Rotators with fixed spray heads, or sprinklers with drip lines — because they water at very different rates and one area would end up flooded while the other stays dry.

In practice, zones also follow the yard: front lawn, back lawn, a side strip. When the solver in the Topoform app builds zones, it keeps each zone a connected group of neighbouring heads, which keeps the pipe runs short.

Don't know your supply flow?

Measure it — it takes a minute with a bucket and a phone stopwatch. The bucket test calculator turns the result into a flow and shows straight away how many heads of each arc fit one zone. Measure at the tap you will connect to, with the tap fully open.

If you do not know your heads yet either, start with how many sprinklers do I need: enter your lawn size and your supply and it gives you both the heads and the zones.

After the zones

Each zone becomes one valve and one station on the controller, so the zone count tells you the smallest controller that could work. Because the count here is a minimum, buy a controller with spare stations, or draw the yard in the app first and size the controller from its zones; Topoform's parts list sizes the controller to the app's zone count plus a spare station. In the Topoform app you draw the real yard, set the available flow at the source and run Auto-design: it places the heads, forms the zones within your supply, adds the valves and routes the pipes, then lists the parts. You can regroup zones by hand afterwards, and every change is checked against the same limits.