Nozzle Calculator in Handy Charts Posted November 25, 2020 Pressure Washer and Jetter Nozzle Calculator (amazingmachinery.com) On the bottom calculator.... Option 1. Add up all your nozzles on the gun, so for a xx03 and a xx02 type in 5 Type the pressure you are getting at the GUN not the pump unless you know for sure you are not getting friction loss. Typically a 3/8 50' hose has zero loss under 5 gpm. This will calculate your total GPM at the gun. Option 2. For a single nozzle Type in a 3 for a xx03 nozzle, 2 for a xx02 nozzle, etc. Then type in your pressure and it will calculate it for you. This is a excellent way to see what you are getting exactly at the gun if you are between the numbers on the typical nozzle chart. I hope this helps!