Three years and still no Gallons per Hour?

@emil It’s great to see that you guys are moving forward on these types of calculators to get people going! I have a couple of questions.

1 - I don’t see the Area when I get to the same screen that you show. What might I be doing differently ?

2 - Would you mind commenting on this post as related to the 1ft x 1ft area assumption ? Had I done that for my case I would have ended up with a PR much higher than necessary to get the recommended deep desert watering that is common here, and recommended by our local resources. It seems that the 1ft x 1ft assumption is good for heterogeneous systems with emitter grids and/or rings, but I don’t see the same application for single point shrubs, etc.

Thanks again, this work is great to see !!!

Hi @azdavidr,

I really appreciate your feedback. With drip lines - area is set to 1 for the calculation because drip lines have a higher pressure than your typical rotor/fixed spray head and do not cover much ground. Hence why this goes straight to a meter measurement test.

If there is a better way that you, @emil, and I can get together, I am happy to get make the changes needed.

@lucasc I see, the turf option has the area but drip doesn’t. That makes sense! As a side note, the drip calculation when choosing US measurements puts out PR in cm/in. I’m not sure that’s what you intend?

@Linn, the wizard and the custom nozzle articles are now linked together. See this article now

@azdavidr Good catch! It’s fixed now :cheers:

I’m not saying you are doing anything wrong. I’m just going through the thought expirement.

So if you had the gph box you would enter?

I’m assuming you would make multiple entries for a single zone and the software does its intergalactic business and computes a mythical number (you didn’t provide enough info) of 60 gallons an hour.

Are saying that you would want to configure flex to apply 120 gallons of water this a 2 hour run time?

Here is my exact process from Water Use It Wisely. The steps below correspond to the same steps in the website.

Step 1: I picked the following average canopy sizes for my larger shrubs and trees, and found the appropriate gallon recommendation

Step 2: Take note of my GPH per shrub and tree as directed by the site. In my case it was one, 1 GPH emitter per shrub, and three 2 GPH emitters per tree. Here’s what they state for step 2.

Step 3a: Use the information from steps #1 & #2 for the entries in the calculator they have in this step. Hit ‘Calculate’, and see the recommended run time.

Step 3b: Hit ‘Next’. They list a table for Phoenix that suggests watering frequency and root depth. I used these to approximate a root depth. Since I had decent values in place for AWC, and with Rachio’s magic, I automatically got the intervals they suggest. Check!

Step 4: I went into the Rachio settings for nozzles, and adjusted the PR down until I got to the suggested 8 hr times for shrubs, and 4.5 hours for trees.


Coudn’t Step 4 be easily spit out by a Rachio calculator once it has the information from step 3 so I didn’t have to make the empirical adjustment to PR? As you well noted, there are comments in the Water it Wisely site about moving the heads out to the canopy circumference and adding heads as the vegetation grows. In my case I haven’t had to add heads beyond the three per tree. Perhaps I got lucky because of the development stage of my vegetation. Our yards also tend to be reasonably dense in terms of the trees/shrubs, so I also think there’s some amount of H2O stealing from one plant to another for those that have longer roots. Don’t tell my neighbor, but I’m pretty sure my large Ficus is drinking up his water too. It’s not ideal, but if Rachio had this type of calculator built into their site I think it would get people a lot closer to a decent starting point, and would minimize the frustration highlighted by this thread. A single-point-emitter Rachio setup calculator like this could (and probably should) have a bunch of disclaimers on it that state the recommended uniformity and placement of emitters. That way people would know that this is an approximation, and the further they deviate from the assumptions the worse their estimate will be.


Glad you posted that–I was just about to. You did a great job with the pics and your explanation!
One final step I took was to use a soil probe to confirm watering depth.

I’ve been thinking about this “gallon per hour” thread and like you, I found the flex daily for the lawn easier than the drip system. Besides, St. Augustine grass is tough and very forgiving, but the drip on the veggies took a lot of “tweaking” to set up so the tomatoes didn’t split and the cucumbers didn’t fry in the blazing afternoon sun.

Funny comment about the ficus. :smile:
My neighbor’s Indian Fig sent huge roots under the fence to my lawn. Now that thing is getting close to 10 ft. tall and the pads on it are over a foot wide.


One thing I’ll note with regards to single point emitters vs. drip rings, The choice isn’t related to laziness or lack of knowledge I believe. I’ve gone to several seminars put on by landscape experts in the valley that seem pretty knowledgeable. They mentioned drip lines but always focused on single point emitters. I believe this is because most of this is pushing for desert adapted landscapes. So you don’t necessarily need a drip ring since for most desert adapted trees you don’t need to water more than 50% of the root ball for the tree to grow.per their recommendations. So a drip ring may be overkill and also a bit of a hassle since you do have to keep moving the emitters out to the drip line as the tree grows.


Which even further complicates a solution. Here in the south we do a ring then apply the emitters where you want them.

We need a GPM based upon meter readings to have an actual minute usage for each zone. This should have been done first because it is way easier and user friendly than a complicated dripper/area calculation.

We need it soon!

@Commuterfisher, are you referring to a GPM field in the app? If so, I’d recommend adding some comments to this product suggestion in how you’d like to see it work.

If you’re just looking for a calculator, the steps listed in a post above can be used to calculate the precip rate using your meter (see meter instructions within the interactive questionnaire for more detail).

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@lucasc For your online calculator that determines precipitation rate of drip emitters, would the 1 sq ft assumption increase with the number of emitters in the zone? I have about 15 drip emitters and they put out in total 50 in/hr from your calculator (my system is a bit over-pressured) ! Should the assumption be 1 sq ft per emitter? So my square footage would be 15 sq ft to bring the precipitation rate down to 3.3 in/hr?

@redwagon If you use the 1 sq. ft. assumption, do a sanity check on your run times once you use the associated PR. I found the watering duration to be vastly lower than what it should be using the 1 sq. ft. assumption for single point emitters. I know the 1 sq. ft. assumptions work for some. Maybe it’s due to desert watering requirements, but I would check your watering times against what you expect them to be. My PR for my 2 GPH drips (3 per tree) is 0.4 in/hr to get the deep watering we require. At 3.3 in/hr my run times would be 8 times shorter than the local (Arizona) recommendation for my trees.

Thank you @azdavidr, just wanted to highlight the error in the online calculator that is assuming 100% of the water in a drip zone is being applied to only 1 sq ft of area. Most drip zones have multiple emitters. Reading through this thread, I understand the arguments for/against 1 sq ft usage, but that area should at least be per emitter in the calculator.

Interesting that you went to 0.4in/hr to get the watering you need with the 2 GPH. I’ve figured out that mine is mostly 1 GPH single point emitters, and I had to go to 0.2 in/hr to get the watering that Water Use It Wisely recommended. I’m not in the desert, but I had been doing 130% of the time to get the watering time that it seemed the plants needed, not scientifically at all, but just based on watching them and how they responded to the water - I had started with 0.5 in/hr when I set the system up (which watered WAY too short - and I had to go to 150% to get to what the plants seemed to like better), then went down to 0.3 in/hr, and after reading through Water Use It Wisely, I’m now down to 0.2 in/hr and I’ve been able to remove the +/- amount and let flex daily do it’s thing.

BTW, the PR = (96.25 (AB))/C calculation made no sense to me with emitters. Assume C=1. I haven’t exactly counted all my emitters, but if I go with 75 1GPH emitters, I come up with 96.25 (75(1/60))=120 in/hr, And if I have 100 of them it’s 96.25 (100*(1/60))=160 in/hr. Neither one of them puts me anywhere NEAR the 0.2 in/hr that appears to be working fairly well! So thank you to @redwagon for getting me to understand that I probably need to make C equal to the number of emitters. So even doing that, I still come up with 1.6 in/hr which would still not get me enough watering time.

Hopefully someone more knowledgeable than I can come up with a formula that works for emitters! At least I was able to back into it using the Water Use It Wisely site. (Yes, I know I can go out and read the meter and it will probably be more accurate, but my meter reads in cubic feet which means yet MORE calculations, albeit easy (1 cubic foot = 7.48052 gallons) - I was just hoping for a simple mathematical way to do it).

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If you are doing this by hand, I found 1 square foot per gallon per hour works best, your mileage may vary

to assume total square footage is 1 makes no sense to me
It should be (96.25 * (75 /60)) / 75 = 1.6 inches an hour.

But this method assumes you ring your vegetation, aka you have multiple emitters per plant.

If you don’t, you need to calculate the square footage of every bush canopy and use that as square footage.

But again this path will be fraught with perils of you are not ringing your vegetation.

Software can only accommodate a certain amount of negligence :frowning:

Even the beloved water wisely site recommends the ring for each plant so if you are not fin plowing that, you need to fall back to square feet of canopy as the area of this equation

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I want it to come up in my application everyday the actual amount of gallons used. This hand calculation is in exact and way beneath such a nice app as yours. I don’t get why you have not made this more user friendly yesterday.

Please make this a priority. Today.

I agree there should be a drip option when setting up the schedule. That is a badly needed addition. I’m actually not a fan of drip irrigation because I’ve seen so many drip installs here that are an absolute mess. But for the more arid western states where drip is so prevalent it is a must to have drip as an irrigation.

Not sure that you live in the desert and use drip extensively. All the water landscape courses teach a method of matching gph to the size of the plant and yes you sometimes have more than one emitter per plant, and then you set the time based on the gph and what is needed for a plant with that size of canopy for that season. All the other calculations are just confusing and have nothing to do with it. By definition a xeroscape watering system concentrates the water only on the plants, not the area - so that just confuses things. You are deliberately not watering the area, but rather just the plant to minimize evaporation and not waste water where you want nothing to grow.

I agree I’m mystified why Rachio will not embrace emitters more fully. Much of the water limited West operates on these principles.