How to design a sprinkler system, step by step

Before you start

Designing a lawn sprinkler system is mostly bookkeeping: how big is the lawn, how much water can you get, which heads, how far apart, how many run together, and how the pipe gets the water to them. Get those in the right order and the rest — digging, gluing, programming — is straightforward. Get them out of order, and you end up with dry patches, heads that barely pop up, or a controller with too few stations.

This guide uses the same rules as the Topoform app, whose engine designs with the Hunter MP Rotator nozzle family. Where a number appears, it comes from the data the engine uses: Hunter's published nozzle figures and the knowledge base it was built from. Each step links to a free calculator, so you can try the numbers on your own yard as you read.

Step 1: Measure the lawn

Start with a plan of the area you want to water. A rough sketch on squared paper is enough, as long as the dimensions are right:

• Measure the outline of each lawn area: the long sides, the short sides and the position of any curves.
• Mark what should stay dry: the house, paths, a patio, a pool, planting beds and trees you do not want to soak.
• Mark where the water comes in — the outdoor tap or the meter — and where a controller could go, usually near a power outlet in the garage or on an outside wall.
• Note slopes and narrow strips. A side yard or a strip along a fence needs different heads from an open lawn.

Treat separate lawns as separate areas: a front lawn and a back lawn split by the house are two shapes, not one. If you have a site plan or an aerial photo, you can trace over it; in the Topoform app you upload the image, set the scale with one known distance and draw on top of it.

For a quick first estimate of a simple rectangular lawn, enter its width and length in how many sprinklers do I need. It runs the app's layout engine on the rectangle and gives you the head count and the zones in seconds.

Step 2: Measure your water supply

Your water supply sets the size of every zone, so measure it before choosing anything else. You need two numbers.

Flow: the bucket test

Flow is how much water the supply delivers per minute. Measure it at the tap you will connect to: open it fully, time how long it takes to fill a bucket of known size, and divide. The bucket test calculator does the arithmetic and gives the result in gallons per minute and litres per minute. Make sure nothing else in the house is running water while you test, and repeat it a couple of times.

You will not design zones to use all of that flow. Leave a margin so the household can still use water and the meter is not run flat out: Topoform designs each zone for at most 75% of the measured flow, the figure Rain Bird recommends for irrigation on a water meter.

Pressure

Pressure is what pushes the water out of the nozzle to its full throw. MP Rotators are rated at 2.8 bar (41 psi). A simple pressure gauge that screws onto the tap tells you your static pressure. Pipe runs lose some pressure along the way, so the static pressure at the tap needs to be above the nozzle rating, not just equal to it. In the Topoform app you enter the static pressure as the source pressure, and the app compares it with what the nozzles need after the losses along the main line.

If your supply is a tank with a pump rather than city water, the pump provides the pressure; the app can size the pump and tank from your zones instead.

Step 3: Choose the sprinkler heads

For lawns, the choice is between fixed spray nozzles, rotary nozzles and larger rotors. Topoform designs with Hunter MP Rotators — rotary nozzles that sit on a standard pop-up body and send out slow, rotating streams. They put water down gently, which suits clay, slopes and lawns where runoff is a problem, and their flow follows the arc you set, so a whole zone waters evenly.

Each model covers a range of throw (Hunter's published figures):

• MP800SR: 6–12 ft (1.8–3.7 m) — narrow side yards and small spaces.
• MP1000: 8–15 ft (2.5–4.5 m) — small lawns and strips.
• MP2000: 13–21 ft (4.0–6.4 m) — the all-round size for a typical lawn.
• MP3000: 23–30 ft (6.9–9.1 m) — large open lawns.
• Strip nozzles spray a fixed rectangle along an edge: the side strip covers 5 × 30 ft, the corner strips 5 × 15 ft.

Pick the size from the width of the area, not from its total size. A long strip that is only a few metres wide needs a short-throw nozzle along its length; an open back lawn can take the larger models. Many yards end up with two or three sizes, each in its own area. Topoform's Pick nozzle size per area option does exactly that: it measures how wide each part of the lawn is and chooses the nozzle that fits it.

Step 4: Space the heads head to head

Place the heads so each one's spray reaches the next head. This is called head-to-head spacing, and it is the single most important layout rule: the outer part of a spray gets less water than the middle, so neighbouring sprays have to overlap to even it out. Heads spaced so their sprays only touch leave dry bands between them.

In practice:

• Corners first. Put a quarter-circle head in each corner of the lawn.
• Then the edges. Fill each edge with half-circle heads, spaced at the throw radius.
• Then the middle. If the lawn is wider than the throw, add rows of full-circle heads inside, again at the throw radius.
• Spray inward. Edge heads spray into the lawn, not onto the path or the house.

The sprinkler spacing calculator gives the spacing for any MP Rotator model and radius, and can show the layout Topoform's engine draws for a rectangle with that nozzle. The flow of each head follows its arc: Hunter publishes the MP2000 full circle at 1.47 GPM (5.6 L/min), a half circle at half of that and a quarter circle at a quarter. Write down the flow of every head on your plan — you need it for the next step.

Step 5: Group the heads into zones

You cannot run all the heads at once on a household supply. A zone is a group of heads that share one valve; the controller opens one zone at a time, so your supply only has to feed the busiest zone.

Two limits apply to every zone, and the lower one wins:

1. The supply. The zone's total flow stays within the share of your measured flow from step 2.
2. The pipe. With the 32 mm poly pipe Topoform designs with, the knowledge base gives a maximum of 14.1 GPM (53 L/min) and recommends designing zones under 11.4 GPM (43 L/min).

Add up the flows of the heads and split them into groups that fit. Keep each zone a compact group of neighbouring heads — one part of the yard — so the pipes stay short. With MP Rotators you can mix full, half and quarter circles in one zone, because they water at the same rate. Do not put rotary nozzles and fixed sprays, or sprinklers and drip lines, on the same zone: they water at very different rates.

The zone calculator takes your measured flow and your list of heads and gives the minimum number of zones and what goes in each. It works from flows alone; keeping each zone a compact group of neighbours on the real yard can take one or two more, which is what the app's Auto-design does. Expect the zone count to grow when the supply is weak: more, smaller zones are the normal answer to a low-flow tap.

Step 6: Lay out the pipes

The pipe network has two parts:

• The main line runs from the water connection to the valves. It is always under pressure, so it should be the sturdiest part of the system. Valves are usually grouped in a valve box near the connection or spread out near their zones.
• The zone lines run from each valve to its heads. Lay them as branches off a central line rather than threading every head on one long chain — a daisy chain loses pressure along its length and the last heads under-perform.

Each head connects to the zone line with a short flexible riser, so it can sit exactly at the edge of the lawn even if the pipe is a little off. Keep pipe runs short and avoid unnecessary bends; every metre of pipe costs a little pressure.

Pipe size matters most on long runs and large zones. Topoform currently designs and prices all pipe at one size, 32 mm poly with 1-inch valves. On a small residential zone that is on the generous side: if you run a smaller size from the tap, keep the zones within the flow your smaller pipe can carry, and check with your supplier. In the app the solver routes a main line from the source to the valves and branches to every head, and the parts list totals the pipe length and the fittings.

Step 7: Set up the controller (timer)

The controller opens the valves one after another. Each zone needs its own station, so the zone count from step 5 tells you the minimum size; a spare station or two leaves room for a garden bed later. Topoform's parts list prices a six-zone controller; if you have more zones or want headroom, pick a larger one.

How long each zone runs depends on your climate, the season and the soil. MP Rotators apply water slowly, so their run times are longer than for fixed sprays covering the same area — that is expected, not a fault. Topoform's results show a daily run time for the busiest zone based on a default watering depth from its knowledge base; treat it as a starting point and adjust it on the controller to your weather. Splitting a long run into two or three shorter starts helps on clay and slopes, where water soaks in slower than it falls.

A rain sensor or a soil-moisture sensor stops the controller from watering a wet lawn. Run the system early in the morning, when the wind is low and less water evaporates.

Do it on your real yard

Every step above can be done by hand, and the calculators help with each one. If you would rather draw the lawn once and let the engine do the bookkeeping, the Topoform app runs the whole sequence: you trace the lawn and the areas to skip, set the source and your measured flow, and Auto-design places the heads head to head, chooses the arcs, groups the heads into zones that fit your supply, adds a valve per zone and routes the pipes. The result comes with zone flows and a bill of materials with quantities and estimated prices, and every head, zone and pipe stays editable by hand. It is free during the beta.