How to Use a Nozzle Sizing Chart
Nozzle size are listed vertically on the left (Yellow). The PSI rating is listed on top (green) left to right. Under each PSI rating the gallons per minute (GPM) allowed by the orifice will be listed vertically. To match the nozzle orifice to your systems requirements begin by finding the PSI rating on top. Follow this column down until you find the gallons per minute rating of your pump. Now look all the way to the left and find the orifice size required by your system.
If the nozzle size is too small, your equipment can be damaged. If the nozzle is too large, cleaning ability is compromised. Note: Nozzle fan size does not effect nozzle size selection
You can also use the Baren's Nozzle Size Calculator