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.
This formula is from
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????