# Figuring out PR for drip emitter zone

I have a question about how to set precipitation rate for a zone that is using drip emitters. In the zone are different kinds of plants - ie, some flowering plants, some shrubs, and these are seoarated by mulch. Each plant has either 2 or 3 2gph emmitters, and this was set up by the person who installed the garden.
I’m not sure how to figure out precipitation rate. I can’t do a a catch cup test, and anyway I know that each plany is getting either 4 or 6 gallons per hour. I can’t use the formula because I donlt have a good sense of the area, since I don’t think I should be measuring the total area because of the large areas of mulch or patio (this would be like using the whol size of a patio as the area being watered in pots on the patio). And anyway, it doesn not seem that the area matters for how long the emitters are programmed to be on - I have played with this variable in the adbanced settings, and it doesn’t change watering time. In fact, it seems that what is important in figuring out watering his how much an individual plant will be getting.
I have looked at the various spreadsheets, and while these are interesting, they depend on knowing how much water you want for a plant before you figure out the PR. I want to start with an accurate PR and see what Rachio comes up with.
Perhaps the formula could be used with by inputting 1) how much the drip is putting out, say 4 gph, and some idea of the area which is covered by the drip. But would that be how deep the water goes, or how far it spreads out underground, or should itjust be the size of the plant?
On the other hand, it woud seem that knowing the drip emission rate would help - is there not a standard PR for a 2 gph head, for instance?
On another matter, I have noticed that the area variable in the advanced Zone settings does not factor into the equation for how long the system should run. Is that true? What is the area used for?
I hope someone can help me with these questions.
Thanks

This thread right here is exactly what you need. @azdavidr put this together to calculate how to convert your emitters to the inches per hour required for Rachio. The excel sheet walks you through the process pretty well, but if you have any questions, post them up!

1 Like

Thank you so much. However, I am familiar with that excel sheet.
What I am interested in is the equivalent if a catch cup test for drip emitters. The Rachio page that discusses how to compute PR gives 2 methods - the catch cup test and the formula. However, the catch cup test (and probably the formula also) is designed for sprinklers that cover an area fairly uniformly. Drip emitters seem different.
The excel sheet developed by azdavidr is excellent, but it is an example of using the formula. In addition, one of the inputs is how much water you want to go onto a plant. So, basically, the spreadsheet works backwards to compute the ideal PR to give a certain amount of water. It also computes an “area”- but it is not clear to me what this means. Hence my second question, which is about what “area” means when applied to single point warer sources, ie drip emitters; and whether inputting a correct area is even necessary within the Rachio app.
Botto line, I am seeking a method to compute PR that uses measurement of water output from drip emitters.

I too have that exact problem - I primarily water with drippers that are measured in gal/hr (gph) but Rachio wants inches/hour. I have been struggling with this for a year, trying to figure out how to increase or decrease the amount of water my plants get

Does a calculator converter exist somewhere for this?

The excel sheet I linked will do that and some…

That excel sheet does give the PR, but bky if you input how much water you want to apply - it doesn’t figure it out from either measuring the output of the drip emitters and using the area. In fact, the area is an ouput of this excel file, not an input.
Not to say that’s it not a great and useful excel sheet, just that I wanted to see if there was another way around the problem.
For example, if there are several drip emitters on a plant, perhaps using the total gpm and the area covered by these emitters?

Area doesn’t play into Rachio calculations at all. It only used to figure out potential water usage and savings on the main screen.

Thanks, that was one of my questions, whether area figured in calculations on the app. And it sounds like it doesn’t figure in the calculation of duration and freqency (which are the important calculations, after all.
However, I was referring to the formula for PR, Pr = 96.25 * GPM/A, where area does figure.
So I was wondering if I know GPM for drip emitters on a plant, what value of A should be used in this formula to calculate PR?