Sprinkler Math: How Many Sprinkler Heads Per Zone?

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If you put too many sprinkler heads in one zone and the pressure drops. Use too few, and you won’t be efficiently watering your plants. Getting the number right is a bit tricky. 

How many sprinkler heads per zone?

Well, there is no fixed number. It depends on the water PSI and GPM ratings of your water supply. The number of zones and the type of sprinkler used also factor into this calculation. 

That’s a watered-down version of the answer. We go into much more details in this article. Stay with us as we detail the process of calculating the number of sprinkler-heads per zone. 

Let’s start cracking that question! 

Picking Out a Sprinkler Head

Before answering “how many sprinkler heads per zone”, you need to pick a sprinkler head. The specifications of the sprinkler head will affect your decision. 

You need to compare the readings for your plumbing system to the sprinklers’ specifications. That’ll help you arrive at a decision about how many you need in each zone. 

There are 2 types of sprinkler heads:

Rotors

A type of sprinkler head that sprays water in a periodic pattern. It either rotates the stream of water or moves it back and forth. 

Sprays

These sprinklers spray water in a fixed pattern. Based on the type of nozzle the spray is either semi-circular or circular. Some spray heads have interchangeable nozzles allowing for either shape of spray.

Each type has its own pros and cons. Rotors cover a wider area and spray a lesser amount of water over a longer period. And they require less maintenance since the sprinkler heads are larger. However, they have longer installation times and are more expensive. 

Spray heads on the other hand are perfect for small areas. They spray a larger amount of water over a smaller region in a shorter period. But they require more maintenance.

To help you a bit more in picking your sprinkler head here are our suggestions:

Product 1
Product 2

Hopefully, you can now pick out your sprinkler head. 

Figuring Out Factors For “Sprinkler Head Per Zone”

Now that that’s out of the way, we can get to the main part. Which is figuring out the sprinkler head per zone count. But to do that, we’ll need to go through a few factors.

Water Pressure 

This is a measure of the force with which the water runs through your plumbing system. The sprinkler will use up different amounts of water based on the available water pressure. 

Most sprinkler systems operate at approximately 30 PSI. But you’ll need to know the specific requirements of your system. 

If you’re facing water pressure problems, you’ll have to dig around a little to be sure. A faulty water pressure regulator may or may not be the problem.

Measuring My Water Pressure

Knowing how it affects your decision is only half the chore. The other half is taking your own readings. This step will require specialized equipment. You’ll need to purchase a pressure gauge. 

First, you’ll need to turn off every faucet in your home. Next, attach the pressure gauge to the faucet closest to your water meter. Then, turn on that faucet, and voila! You have your water pressure reading. 

Make sure to turn off the faucets individually. Using the main shut off valve will turn off the water supply entirely. That will turn off the waterflow entirely. While you’re at it, take a look at the valve. The main water shut off valve replacement cost could be high.

Flow Rate

The flow rate is a measure of the water flowing through the system at any time. 

Measuring My Flow Rate

You won’t need any specialized gear for this measurement. Just crank a faucet to the max and leave a five-gallon container under it. Start a timer exactly when you turn on the faucet.

Stop the timer when the container is full. The amount of water over the time taken will give you the required result. In this case, it’ll be 5 Gallons divided by the reading on your timer in minutes. 

Let’s say that it took 20 seconds to fill the 5 gallons. Then your flow rate will be [(5*60)/20] gallons per minute. 

How much water the sprinkler heads use depends on the water pressure. Combine that and the flow rate of your system and you have your per zone limit. 

Assume your plumbing system has a flow rate of 10 GPM and 30 PSI pressure. And the sprinkler you opted for uses 2.5 GPM water at 30 PSI. This would mean you can use 4 sprinkler heads per zone.   

Comparing the GPM and PSI readings will give you the maximum possible number of sprinkler heads. But, that doesn’t tell you how many you should use. For that figure, you’ll need to do a bit more digging. 

Zoning 

The major calculations for determining the number of sprinkler heads are done. But more often than not, that won’t be enough to make a decision. You’ll need to calculate your zones properly too. 

Things to Remember 

You’ll need to remember the following when calculating and mapping your zones:

  • The zones must be populated with plants with the same watering needs.
  • The number of zones can’t be less than the recommended number.

You might want to identify what type of lawn grass you have to properly water it. This will help you in figuring out the zoning and watering needs.

Mapping the Zones

Figure out where your sprinkler heads need to go after measuring your yard. Take into consideration the placement of your plants while doing that. Consider the circumference of the spray from your sprinkler head too. 

Halve the sprinklers’ spray circumference and that will be the distance between two heads. With that information map out the sprinkler heads all over the yard. Get as many sprinklers as it takes to cover every plant’s watering needs.

Now, sum up the total GPM of all the sprinkler heads at the PSI available. Then divide that number by the flow rate of your system. And that is how many zones you should have. 

Getting to the Final Number

Okay, so you have all the numbers you need. Now, you have to first map out your zones considering the number of zones you need. 

Then you have to place the sprinklers maintaining the optimal distance between each. The optimal distance is half the sprinkler’s spray circumference. 

There is a possibility that this will give you a different per zone count. This count may be higher than the one you got from comparing the GPM & PSI. If that’s the case then you’ll need to increase the number of zones. 

That covers it all.

FAQs

Question: What to do to avoid pressure dips?

Answer: It’s simple. Just cut your run time in half. If you have a half-hour run time for each zone, drop it to 15 minutes. 

Question: Why aren’t my sprinklers spraying enough water?

Answer: That’s because you have exceeded the max number of sprinkler heads per zone. The controller runs all heads in a zone at once. To keep all the heads spraying it will drop the pressure if needed. 

Question: What’s the best time to run the sprinkler system?

Answer: There is no best time for running the sprinkler system. When you use the sprinkler doesn’t affect its performance. But if you run it in the morning it gives you an added benefit. It keeps the ground cool.

Conclusion

With all these calculations you can answer how many sprinkler heads per zone you need. We know the process is a bit lengthy. However, it’s fairly intuitive and doesn’t require much work on your part.

So get your equipment out. Measure the necessary values. And figure out the number of sprinkler-heads per zone. When that’s done you can put in your sprinkler system and have a greener yard.

Good luck!

Richard Allen