Gathered data, need help figuring out drip custom nozzle rate


I finally had a day where I could gather the data on my two drip systems that I’m most concerned about. I’ve been guessing the PR rate, and I’d like to get it set correctly.

Here’s the data I collected:

Zone 9 (50 - 75 emitters), ran for 60 minutes, used .225 CF
Zone 10 (75- 100 emitters), ran for 60 minutes, used .35 CF

All emitters are one per plant. Yes, I have a lot of plants in my beds.

According to my water bill, 1 ccf = 748.05 gallons


Zone 9 used 168.31 gallons in 60 minutes
Zone 10 used 261.81 gallons in 60 minutes

I then followed this link from a posting of @emil

I selected Imperial and drip, put in my 168.31 gallons and 60 minutes tested and it calculated “Your Precipitation rate is 269.5000in/hr” – I don’t think so! This would never work! and 261 gallons gets “Your Precipitation rate is 418.6875in/hr” — sure looks like this calculator is missing something for drip systems or I’m not getting something.

I currently have both zone 9 and zone 10 set with a custom emitter of .2 in/hr, guess work on my part because that gets me 80 minutes of watering time on each zone (which appears to be about right from Water Use It Wisely). Zone 10 waters 155% more than zone 9, so if I have 60 emitters in Zone 9, that would be 93 emitters in Zone 10, which might be about right. Do I need to accurately count the number of emitters and add that into the calculation? (And of course they are a mix of 1/2GPH, 1GPH, and 2GPH emitters, which is why I decided to do the test to see actually how much water is getting used because I thought I would be able to back into the custom nozzle I needed). My thinking was that each emitter is one per plant, so it shouldn’t make a difference

Is there a way to go the other direction? Saying that an emitter that puts out .2 in/hr will use xx gallons of water?

I normally like math problems, but my head is spinning!!!

@emil, @Lucas, @franz, @benblackmer, @plainsane, @azdavidr or anyone else, can you help me figure this out?

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I don’t see how that calculator could provide you the rate without the known area. Maybe it defaults to 1 square foot for area? If that is the case then I think you would also need to divide the total gallons by the number of plants/emitters in the zone. Otherwise the calculator is assuming you are placing all the water into a 1 square foot zone.


Omg dude exactly. Everybody in the drip world just refuses to acknowledge how important area is to the formula for pr, and how important pr is to rachio.

I figure 1 foot per gph, that doesn’t work for a lot of systems, :frowning:

What I recommend is compute the area of shadow at high noon, use that as your footage.

I think this is my last drip post I’ll make, I’m exhausted.

That rachio tool assume area of 1 foot which is wrong.

linn, this time is a static equation, add up all your gph, then use 60 minutes time in the equation, use the area of shadow created by your plants as the area and that is your pr.

But from what I can tell from other posts, the emitter or emitter count is not sized effectively with the plant so you are going to have some variance where some plants get more than needed and others too little. Maybe I’m wrong and conflating other ppls posts as yours.


@Linn, here is how I solved this problem. First, I totaled up the output of all of my emitters. I also have a mix of 0.5, 1.0, and 2.0 gph. This total came out to 15.5 gph (I only have 16 emitters). Next, I checked the usage of the drip zone at the water meter. This came to 34.8 gph (Also have very high pressure, working on fixing this).

Next, I wanted to know approximately how much each emitter is actually putting out. So for 0.5 gph : 0.5 gph emitter / 15.5 total gph * 34.8 actual gph = 1.12 gph flow of my 0.5 emitters. Did the same for the 1.0 and 2.0 emitters also (or just multiply 1.12 times 2 and 4). Note: this approximation assumes all emitters distribute evenly. I would guess different emitter brands, elevation in system, etc, can change the output rates, but I can live with that error. Skip this if you feel your emitters are putting out water equivalent to their rating. It was clear that mine were not.

Now you need to decide how much water you want to put on your plants. Either determine this from how much you have historically watered, or I just assumed the plants need about 1 gallon per foot of canopy diameter with about 6" of root depth. I used the default 1.0 in/hr emitter, and the app gave me a time of 32min. This provided a little over a gallon of water for my 1.0 emitters (32min / 60min/hr * 2.24gal/hr = 1.19 gallons). Right where I wanted them. If you need more water, create a custom emitter with a lower precipitation rate. This will make Rachio run the system longer. Note the new run time, and use that to calculate the water amount per plant. Adjust until it fits your needs. Also, use different or multiple emitters for different sized plants

To get accurate usage from the app, calculate square footage to input. I used the 1.0in/hr emitter rate and 34.8gph/60 = 0.58 gal/min into the following equation:

AREA (sq.ft) = water usage (gal/min) * 96.25 / PR (in/hr)

I get 34.8 sq ft. Input this into the zone settings, and Rachio will give me accurate usage data.

Hope this did not confuse you more. Hopefully Rachio will more fully support emitter zones in a future release, until then, this workaround has been fine for my setup.


yes, @plainsane I get (and already knew) that the calculation doesn’t work. I just wanted to make sure that the Rachio folks knew that the calculation didn’t work so that they wouldn’t mislead other people.

Later this fall, when I’m in town again, I’m going to attempt to count and mark every emitter. It’s going to be a time consuming job, and it’s just too dang hot to do right now. (I can just count the plants, but I really want to know where there is more than one emitter, the kind of emitter, and in a few spots I have plants that have died and I need to mark the emitter so that I can either put in a new plant or plug the hole).

My guess is that there are many others with setups like mine – one emitter for each plant. In almost all cases, my larger plants have the 2 GPH emitters, so there is some compensation. And one of my trees on the drip system actually has a ring around it!

Here’s a pic of one of my zones; The pic was taken in June, so many of the areas are different now as the plants have grown over the summer.


@Linn, perfect, thank you for taking these measurements. As time consuming as this data is to collect, it’s critical for crunching the numbers. Assuming we use the high & low counts of total emitters in the calculator, I crunch the following custom nozzle values:

Zone 9 @ 50 emitters = 5.4 in/hr

Zone 9 @ 75 emitters = 3.6 in/hr

Zone 10 @ 75 emitters = 5.6 in/hr

Zone 10 @ 100 emitters = 4.2 in/hr

The correct value is probably somewhere between these high & low values, however these ranges seem reasonable given the data provided. For baseline values, most drip nozzles (and zones) should fall between these values:

Those are some Biblical drip zone values! I think we’re applying the 1 sq foot for area incorrectly here. That recommendation is for users that only know the nozzle application of one drip emitter and want to make the best guessimate for a custom nozzle. It uses the 80/20 rule, which isn’t the route you’re going. We’ll address this in the nozzle calculator instructions to help clarify.

@JPedrego, great comment and insight; you hit it on the mark. So using the 1 square foot rule, if you’re using the total water output for a zone, you’ll need to count the total number of drip nozzles in said zone.

I feel ya. These are all great conversations that help us to better understand how users interact with our product and ways to improve it. Drip zones are hard. There’s a reason why the smartest people in irrigation technology have PhDs. :books:


@emil I usually disagree on the 1 sq. ft. assumption and will again here. I doubt believe that the 3.6-5.4 in/hr numbers are reasonable if @Linn doesn’t have emitters spaced out in an even pattern spaced 1 ft. apart. If he has single point emitters, like many of us do, or even 2 or 3 emitters per plant on larger vegetation, the pr is way too high.

If he had a perfect design then maybe, but he doesn’t. Using a larger area in the calculation compensates for a non-ideal design and decreases the pr. I use 0.4 in/hr for 2 gph emitters and 0.2 in/hr for 1 gph heads to get the run times suggested by our local authorities. I don’t know if some of my disconnect is due to requirements here in the desert, but I do know if I used numbers that high I would have a lot of dead plants.

At minimum every time you guys state that 1 sq ft assumption you should ask if they have evenly spaced emitters covering the diameter of the root zone. Ideally I would like to at least see an option to calculate the pr based on the desired total gallons of water delivered to a plant. The math is easy using GPH (time = gallons/gph), but then you could back calculated the area parameter to accurately get water usage calculation from your software.


@emil, I tried a custom nozzle with your 3.6 inches/hr. It would water for 4 minutes. For my 1GPH emitter, that would give the plant about 1 cup or 8 oz. of water. My plants would be dead in less than a week.

I recognize there are many different ways of setting up drips. What is most commonly done in my area is that plants are set up with one emitter per plant. They are not spaced evenly 1 foot apart, they are spaced the way the plants are out in. That is why I was careful to say that I had 1 emitter per plant.

I am very grateful to @azdavidr for pointing me to the Water Use it Wisely site. What they have documented makes logical sense. I ended up defining a custom nozzle with .2 in/hr which seems to work well. As you can see, that’s WAY different than the 3-5 in/hr your calculations came up with. I did the exercise of measuring the CCF’s so that I could try and dial it in closer/better. I would just like to see this easier for other users.


@emil. How do you reconcile you 3.6 pr rate in this thread versus the 0.4 in/hr pr recommendation that was posted here? That happens to be exactly what I ended up calculating on my own.

If it’s pressure regulators that make a difference then should that be accounted for in the settings somewhere, maybe with a new nozzle type?


I don’t want to stir any pots but I use 3.2 in/hr based off Rachio calculators for my 2 GPH and here’s a look at one of my lantana and orange jubilees. They did fine previous summers with my dumb controller, but they have looked like this all summer. My settings are as accurate as possible so something is amiss here.


@Modawg2k How long and how often are they watered, and how does it compare the the Water Use It Wisely site?


Rachio has my drips run for only 15 minutes and then every 3 days or so. For 1’ canopy shrubs, looks like water wisely says i should water for 30 minutes on 2 GPH drips. For settings, I dropped AW to 0.1 since it’s much more sandy than my grass.


I think the canopy dimension they ask for is diameter no? From the pics they seem to have diameter larger than that.


@Modawg2k I figured I’d post my moisture graphs so you could compare if you wanted to. I add about 7 gallons per per plant, per watering I think. I’d say the summer average was about once every 8 days. These are with Monsoon activity so it’s slightly skewed.


I’m pretty sure that thing is way off, the way y’all have these setup, I would be amazed if your pr goes about .4 in/hr


@azdavidr yeah yours looks a lot different than mine, here’s next week with no rain in the forecast. Since I have 2 shrub zones I think I’m going to play around with PR to compare on both of them.


Take that bush there, I would put that area at 3 square feet so that gives us a pr of .9 inch/hr with a 2gph emitter


@azdavidr @plainsane check out this difference between the default 0.5 and the Rachio calculated 3.2


@azdavidr Yep, that’s why I keep griping about the 1 sq. ft. assumption.


I’m sure you’ve guys talked in depth about this, but can you show me the calculation to figure this out? Also how did you come up with 3 sq ft?