# Precipitation rate calculations

I’m confused about how to calculate precipitation rates.

To collect data, I used the standard .Orbit catch cups with a 16 square inch opening on the top. For each zone I put out 12 of them and ran the zone for 20 minutes.

Here is an example zone.

Total water collected in 12 catch cups = 359ml or 21.9cu. in. That is an average of 30ml or 1.83cu. in.

When I enter those values into the Rachio online calculator it results in 5.5 inches/hour.

This seems incredibly high as the Rachio default for a rotor head is 1.5, and the system will not permit an entry over 5.0

On the other hand, if I use the formula of (average volume/catch cup area) * 0.06 = PR for the run time I get 0.09 inches in 20 minutes and 0.27 inches per hour.

This formula comes from aces.nmsu.edu/pubs/_h/H510.pdf.

Similarly, the formula of (3.66 x average catch can volume in mL)/ Run time x 16
also gives me a rate of 0.27 inches per hour.

The advertised specifications on my Hunter and RainBird rotor heads indicate and average precipitation rate of 0.3-0.4, so those last 2 calculations of 0.27 make a lot more sense than the Rachio 5.5 result.

What do I not understand???

Did you plug your ml’s into the orbit’s website: http://irrigationaudit.hydrorain.com/get-started/#/stations/getStarted

Thanks for the response. However that link doesn’t seem to work. Maybe their server is down.
The other Orbit url at wateringschedule.com calculates efficiency but not precipitation rates.

I think their site might be screwy right now because it can’t find Phoenix in their system. Anyways, when you get to the screen that shows your results and zone efficiency, click on each zone and it’ll take you to a new page (granted that their site is working correctly) and it’ll give you detailed information including PR