GPH flow rate to Inches Per Hour

Most all of my irrigation is drip irrigation with individual 4GPH emitters on each individual plant. Most plants are 2-3 feet apart. To get the Rachio Flex program to work I need to tell it what the flow rate of the emitters are in inches per hour. How do convert 4GPH into inches per hour to set up each zone?

A complex question, IMHO. To do Nozzle Flow inches per hour right, you need the total flow for a given period (4 GPH x number of emitters would work), and Area being watered (possibly your total drip irrigated area or assume a circle around each emitter) and calculate from there (which I could help with, if you like). You could then use any method of schedule, including Flex Daily.

Another method would be knowing how much water per week you would want each plant (with its 4 GPH emitter) to get. Say, 6 gallons per week, then divide that by 4 GPH and get 1.5 hours per week watering, so set a fixed schedule of 90 minutes once a week, ignoring nozzle flow. While that wouldn’t work for Flex Daily, using Flex Monthly or Fixed with Seasonal Shift ON would give your drip system more water in hotter weather.

But if you have a single plant that is not within 3’ of another plant, and you have a single emitter on that plant that puts out 4GPH, why do you need to calculate the inches per hour for the entire zone? It would seem that essentially each plant is on it’s own zone, and that plant is getting 4GPH.

I don’t understand the need to calculate the number if emitters on each zone to figure this out.

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That’s why I said it’s a complex question. To properly calculate the Nozzle Inches per Hour, you need to know the total water IN INCHES applied per hour. In this case, you’d calculate the Inches by taking the Gallons per Minute of all the emitters in your zone, divide it by the total area in square feet of plants being watered in that zone, and multiply by 96.25. Gallons per minute is pretty easy: # Emitters x GPH per emitter (4) / 60. Square feet of plants is more complex. Are the roots in that 2’ diameter bush 1’ in diameter or 2’ diameter (or 3’). I’m sure they will vary with size and root depth/width. That is one way to do it, but I think you’re doing a lot of guessing that way.

The other way I mentioned is determine how much water you want each plant to get, and use your emitter size to determine the time to water, ignoring the Nozzle Flow.

As to why you need to calculate the inches per hour for the entire zone, is that Rachio uses that figure (VERY important) to determine how long to water. If you can calculate minutes directly, you don’t need to worry about the Nozzle Flow.

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Couldn’t you just look? Skip the math. After an hour of watering an area with an emitter, dig down and see how many inches down it watered. No complexity at all.

This topic revisits a fundamental problem with the Rachio UI. The parameters for configuring a zone are based on the assumption that the zone is watered uniformly, such as a lawn or dense plantings with spray irrigation. Precipitation rate (which now is weirdly named “nozzle inches per hour”) is suited to that type of irrigation but is not meaningful for point irrigation, such as drip or bubblers.

Point irrigation is based on applying water at a known rate to a plant with a known canopy and root area.
Why should a user need to do calculations (assisted with a calculator spreadsheet) in order to enter these parameters into a UI that is based on an entirely different model for watering? This makes the process way too complicated.

The Rachio UI already asks what type of irrigation I have. If the answer is drip or bubbler, it should ask for inputs that are meaningful for that type of irrigation, such as flow rate, number of emitters, size of the plant, and anything else that is relevant. Rachio should then convert those inputs to whatever internal model it is using to make watering decisions.


I just switched from SkyDrop yesterday due to sometimes the system not watering (hardware issue or Wi-Fi issue?). Rachio plugged in and worked immediately! I was very surprised to not see emitter GPH like on SkyDrop. SkyDrop allowed you to indicated what type/how many emitters and would assist with calculating the watering times. My entire system with 4 zones is all drip/emitter irrigation. For now I am just going to try the fixed schedule and set the times manually since the conversion thing seems way too complicated. I don’t have an issue counting and identifying all my emitters/sizes on each zone. The rest seems complicated. Wish it was as easy as SkyDrop was.

It would seem that knowing emitter GPH and soil type would determine how wide the water would spread and depth it would penetrate. I presume that based on soil type it is known the depth that the moisture will penetrate for various inches of rain. While knowing that the length of rain time (or drip time) is a factor. Can’t that be converted in the settings?