# How does Rachio 3 calculate irrigation amount in Soil Moisture chart?

How does Rachio 3 calculate irrigation amount in Soil Moisture chart?

For example, it says on 5/1 that it expects an irrigation event of 0.25 inches via Flex. How does it calculate this amount? I ask because it could just be the average inches per hour we input, or does Flex run longer than that in order to account for the efficiency factor? In other words, is all of my zone getting 0.25 inches (and some much more), etc…?

Similarly how does Rachio calculate gpm used by a zone?

Thanks!

The schedule has determined that .25 inches is the amount needed to fill your zone irrigation “bucket”.

Once filled it then measures daily depletion.

The .25 inches is derived from root zone depth, soil type, and nozzle precip rate/hr.

Here is some more useful information on flex daily schedules.

GPM is an estimate based on zone size and precip rate.

Right, so does the controller think it put down 0.25 inches on average, or did it try to put at least 0.25 inches everywhere? Or something else? The sprinkler efficiency setting tells the controller it has to water longer to get enough water in the entire zone, so if it wants to put 0.25 inches everywhere, then other places would get more than 0.25 inches (unless the efficiency is 100%).

Efficiency is baked into our watering equation and how we determine that if we need to put down .25 inches it will take X amount of time. We use root zone depth, soil type, and allowed depletion to determine the bucket size. We then use nozzle precip rate, efficiency, and a scheduling multiplier to then determine how long the system needs to run to fill the bucket up .25 inches.

Hope this helps!

Rachio first calculates how much to water for each irrigation event for the zone using this formula:
Irrigation amount of water (in) = Available Water (AW) * Zone Root Depth (ZRD) * Allowed Depletion (AD)

Then it converts this to watering time using this formula:
Watering Time (min) = 60 * Irrigation Amount (above) / (sqrt(efficiency) * nozzle precipitation rate)

Once the parameters are configured, the amount of water is fixed, and from what I have observed, Rachio does not attempt to refill moisture level to 100%, but instead will water this fixed amount when it anticipates moisture level will hit the Allowed Depletion level on that day.

It might water less than this amount though if the moisture level would exceed 100%. In that case, it will cap watering time to reach 100% moisture level. I think this might happen if you don’t have Daily Flex schedule running every day.

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Thanks! That seems to work out.

Do we know how it calculates the gallons used? Is it something like:

gpm = (precip rate [in/hr])*(area [sf]) / 96.25)

gallons used = gpm * (watering time [min])?

We use this algorithm to derive estimated usage.

Thanks! That article says how to get precip rate. I’m assuming you use the same formula to get to gpm, and then multiply gpm by minutes. That’s what I tried to do above…

Personally, I have it set to show usage in time and not in gpm because I haven’t gone to calculate square footage for each zone and measure accurate precipitation rates. Also, an area might be covered by sprinklers from two different zones.

I would like one day to install a flow meter and connect it to Rachio and get accurate water usage measurements instead of estimates.

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Because I am Lazy. Ignore the poor conversion tactics used from metric to imperial.

/* https://www.sprinklerwarehouse.com/DIY-Calculating-Precipitation-Rate-s/7942.htm */
protected Double calculateLiters(IZoneDetail zone, int durationInSeconds) {
double sqFootage = zone.getSqMeters() * 10.7639;
double inchesPerHour = zone.getMmPerSecond() * 141.732;
double galsPerMinute = (sqFootage * inchesPerHour) / 96.25;
double gallons = (durationInSeconds / 60.0) * galsPerMinute;
return new BigDecimal(gallonToLiterConverter.convert(gallons)).setScale(2, RoundingMode.HALF_UP).doubleValue();
}

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Thanks to you both. I agree the gallons used isn’t perfect, but it was surprisingly close for the last two month periods I checked. Within 10%, which I think is pretty good considering all the variables.

I wanted the wireless flow meter, but my notify when available request ended with the no longer available notice. That was really frustrating and I was already starting my large project and didn’t have time to research other options, so went without any meter.

U.S. should convert to metric…

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“U.S. should convert to metric…”
There have been a number of feature requests for this, unfortunately too many redirects, timeouts and 404 errors resulted in this not being implemented

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