Well you implicitly assumes that the sprinkler heads are installed according to spec for coverage areas.
It’s a fantastic starting point for people to dial in a flex schedule. Next step I’d take beyond that is a catch cup test.
You are talking about as many potential variables taking GPM readings from your flow meter or main water meter and assuming that it is getting evenly distributed over your yard. Wouldn’t you agree?
change to the metric system? 
I have 2 areas with the same heads and the same nozzles on them.
One is 4100 soft the other 5800 sqft. Obviously the Nozzle Inches Per Hour are drastically different in those 2 scenarios. That is why I don’t think it is a very good idea to use that. What I put together is much closer to a reasonable ball park. and only takes a few minutes to get to. You can use cups to verify that it is close to what you are getting in reality. If you like you can do a cup test to confirm, but as I have said, cups don’t seem very reliable in my experience.
Is it that obvious though? I’m going to make the assumption that you don’t have the same number of sprinklers in each of these zones. I’m not arguing that your way is wrong at all, but in all the irrigation systems I’ve dealt with (and I’ve done a lot), the manufacturers PR spec’s are usually pretty damn accurate if the system is installed correctly and spray overlap is set correctly. And the reliability concerns you have with the catch cup tests I think stem from the almost inherent inconsistencies you see in real world installations.
Oy vey! This thread is giving me a headache:flushed:
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maybe that why its called a flow “meter” 
Why enter the inches per hour when gpm and area would give you that data.
e.g. 42’ rotor throw @ 3.0gpm doing a 180 degree arc equates as follows
pi 42 squared divided by (360/180) = 2771 sq feet
3.0gpm * 60m = 180gph
180g = 24 cubic feet
24/2771 = .0087 feet of water or 0.104" (per hour) @ 100% efficiency
No wonder people complain about the default value of 1.0 nozzle inchs per hour.
You would need a 30gpm nozzle.
Also, if the optimal rotor setup is “rotor to rotor” how does the system know about overlap which can more than double the water in a given area.
That’s why I say utilize the manufacturer’s specs. They calculate PR based on overlap, usually including multiple overlap patterns.
Well, PR in/hr is a function of GPM and area (plus a few other things).
Also, I’m not in a place to work it, but I think your math is off slightly. But,I will agree that the 1"/hr is a tad much for most residential rotors, there are plenty of them capable of it. Here is a link to the Hunter I-20 series rotors, and PR can range anywhere from .27"/hr (1.2gpm) -1.49"/hr (14.8gpm) @ 180 sweep, factoring in overlap. I’d say the I-20 is a more commercial rotor, but still within reach of the average homeowner…just as an example.
Could you share your excel spreadsheet? 
Tom, I wish I could. I can’t upload anything but images.
Total Gallons / Hour =D4* C4 *60
Gallons / SQFT / Hr =E4/B4
inches / SQFT / Hr =F4*$G$1
The G1 field contains “inches / gallon / SQFT” = 1.6042
If you need additional info I can try to share it.
Math isn’t off, however the gpm may be.
Apparently a Rainbird 3.0gpm nozel flows 5.7gpm @ 65psi (per rainbird spec sheet included with 42SA+)
Interestingly the replacement nozzle set sheet shows completely different nozzle flow numbers: 3.0gpm @ 65psi = 3.8gpm (v.s. 5.7gpm on the included sheet)
equally interesting, the same 3.0gpm nozel is rated at 3.3gpm @ just 25psi on the included sheet, but 2.3gpm on the nozzle card.
Rachio offers a simplified equation of
PR = (96.25 * gpm) / area
Numbers match mine above.
PR = Inches/hr = (96.25 * gpm) / area
In summary they use PR and Inch/hr interchangeably
Why the Rachio Advanced settings ask for both PR and area is unknown. I assume PR is used for application rate, and area is used just for mental reminder / reference maybe?
Thanks!
How did you get the value for G1 field (Inches / Gallon / SQFT)?
I actually measured the GPM for each nozzle to confirm what it was using a bucket and measuring output for a minute.
Math:
1 Cubic Foot = 7.48052 Gallons
so if I want to know how many Inches / Gallon / SQFT
12 inches / foot:
7.48052 Gallons / 12 = 1.6042 Inches / Gallon / SQFT
They will utilize area if you want to know gallons used on the home screen, and an estimated gallons “saved” based on weather skips. It isn’t used anywhere else.
Sorry, I don’t get it and “Inches per Gallon per SQFT” does not make sense to me at all… 
Is it possible that you meant:
Math:
1 Cubic Foot = 7.48052 Gallons
so if I want to know how many Cubic Inches / SQFT
12 inches = 1 foot
7.48052 Gallons / 12 = 1.6042 Cubic Inches / SQFT
Tom, if you look over my spreadsheet and calculation the units are correct. Let me see if I can help to clarify it.
Each Gallon of water that hits 1 square foot is 1.6042 inches.
My inputs are:
SQFT
Sprinkler Heads
GPM / Head
Initially I use the Sprinkler Heads and the GPM / Head to calculate total (Gallons / Hour) for the Zone.
I then divide (Gallons / Hour) by Square footage to see how many Gallons are dropped per square foot.
(Gallons / Hour) / SQFT
I then have to convert that into (Inches of Water / SQFT / Hour) as that is what Rachio takes as an input.
That is where the 1.602 Cubic Inches / SQFT comes into play.
The number that is generated gives me that Nozzle Inches Per Hour. Aka how many inches of water over an hour hit this zone.
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Ah okay… got it! 1 gallon of water on 1 SQFT fills this area 1,6042 inches in height if the area was a container.
My missunderstanding comes from where you said:
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right, but we use that and say, ok, let’s say we have 360 gallons an hour being sprayed on 2200 sqft, how many inches are we spraying across that area?
And that calculates out to be: .262 inches / hour.
or 300 gallons over 4,100 sqft and that is .117 inches / hour.
That really helped me understand running times etc. too as the general rule of thumb is that lawns need 1" of rain per week.
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