Our nozzle types use precipitation in./hr which can be calculated using a catch cup test or knowing your gallons per minute, or by picking the closest nozzle type (we use industry standard defaults for in./hr).
If you use a catch cup test it will tell you precip in./hr as well as efficiency which measures all of your heads application (efficiency takes into account overlapping heads, 360 vs 180, etc.)
Catch cup instructions
Qucik and dirty
http://www.sprinklerwarehouse.com/DIY-Calculating-Precipitation-Rate-s/7942.htm
A short video
If you know GPM
Hope this helps
