It depends on the system of measures you use, either U.S. customary units (inches, pounds, etc.) or metric (mm, kilograms, etc.).
If you are working with U.S. measures, the electrodes for SMAW are usually in 1/32 inch increments. GMAW electrode is 0.030, 0.035, 0.045, 0.052, 1/16 inch, etc. So if I stay with the GMAW process and used 0.045 inch for the PQR, I could use a range of diameters of 0.035 inch to 0.052 inch in the WPS.
Hope that helps.
Best regards -Al