There are 4 methods:
- Use the Rachio default value for your sprinkler head type (least accurate IMHO).
- Use the head manufacturer’s specs for your heads, allowing for pressure and distance range.
- Do a test using Catch Cups (time consuming and results VERY dependent upon cup location).
- Calculate from GPM used and Area being applied to (best AVERAGE method, does not tell about high or low water areas).
I use #4. Using your water meter, measure how many gallons of water are used during a given period of time (Total gallons used divided by minutes on) and Area in square feet for the area being watered (can be measured, use Rachio app with version 3, use Google Maps add-in, etc.), then use the formula above to calculate Nozzle Flow Inches per Hour (Flow GPM / Area (sq ft) x 96.25).