How many sprinklers do I need?

What this calculator does

Most "how many sprinklers" calculators divide the lawn area by the area one sprinkler covers. That number is always too low, because a sprinkler layout is not about area — it is about edges and overlap. Heads on the edge of the lawn spray inward in half circles, heads in the corners spray quarter circles, and every head has to reach its neighbours so the lawn gets an even amount of water.

This calculator does not use a rule of thumb. It draws your rectangle and runs Auto-design, the same solver the Topoform app runs when you click Auto-design on a drawn yard, with the Pick nozzle size per area option switched on and a city-water supply. The answer is the layout that solver produces: the number of heads, the nozzle model and arc of each one, how they are grouped into zones and the flow of every zone.

How the heads are chosen

The catalog is the Hunter MP Rotator range: MP800SR, MP1000, MP2000 and MP3000, plus side-strip and corner-strip nozzles for narrow beds. The published throw of each model sets how far apart the heads go:

• MP800SR: 6–12 ft (1.8–3.7 m)
• MP1000: 8–15 ft (2.5–4.5 m)
• MP2000: 13–21 ft (4.0–6.4 m)
• MP3000: 23–30 ft (6.9–9.1 m)

With Pick nozzle size per area on, the solver looks at how wide each part of the lawn is and uses the nozzle whose throw fits that width. A wide open lawn gets the larger rotors; a strip along a fence gets a short-throw model or the strip nozzles, which spray a 5 × 30 ft band from one side. That is why a long, narrow strip often needs more heads than a square of the same area — the heads are smaller.

Heads are placed head to head: each spray reaches the next head, which is the spacing that gives even watering (the spacing calculator explains why). Edge heads get half circles, corner heads get quarter circles, and the middle of a large lawn gets full circles.

Why the flow of every head matters

MP Rotators are matched-precipitation nozzles: a half circle uses half the water of a full circle of the same model, and a quarter circle a quarter. Every head on the lawn therefore puts down water at the same rate, whatever its arc — and you can mix arcs freely in one zone. Hunter publishes the full-circle flow at its rated pressure of 2.8 bar (41 psi); for an MP2000 that is 1.47 GPM (5.6 L/min).

The calculator adds up the flow of the heads in each zone. That total is what your water supply has to deliver while that zone runs.

Why the lawn is split into zones

A sprinkler controller opens one valve at a time, so only one zone runs at once. The pipe limits how much one zone may draw: with the 32 mm poly pipe and 1-inch valves the engine designs with, a zone stays under 11.4 GPM (43 L/min) by design and never goes over the hard limit of 14.1 GPM (53 L/min).

If you know your supply flow, enter it. The zones are then also capped at 75% of the measured flow, leaving a margin for the household drawing water at the same time — the rule of thumb Rain Bird gives for sizing irrigation on a water meter. A weak supply means more, smaller zones. If you leave the field empty, zones are sized by the pipe only. Not sure what your tap delivers? Do the bucket test first — it takes a minute.

How to read the result

• Sprinklers and zones — the head count and the zone count for your rectangle.
• The table — each nozzle model and arc with how many of them you need and the flow of one head. This is the start of your shopping list.
• Zones — the heads and the flow of each zone. Every zone gets its own valve and its own station on the controller.
• The busiest zone — the flow your supply must keep up with. If it is more than your tap or meter can give, enter your measured supply so the zones come out smaller.
• The preview — the layout to scale, with each head's coverage circle. Overlap is intended: that is head-to-head coverage.

What the calculator leaves out

A real yard is rarely a clean rectangle. The calculator does not know about the house, paths, beds, trees or the spot where your water comes in, and it does not draw pipes or price parts. It is a quick estimate for a simple lawn.

For your actual yard, open the app: trace the lawn over a site plan or an aerial photo, mark the areas to skip, and run the same Auto-design. You get the heads, zones, valves and the pipe network on your real shape, plus a bill of materials with quantities and estimated prices — and you can move, add or delete any head by hand afterwards.