In my experience, it wasn't until my
Flaccid Girth was in excess of 5" (mid-shaft specifically because that's the surface area making the most contact with my pants) where the bulge started to show.
There are other ways of improving bulge, including going "commando" (freeballing) and wearing thin fabrics that "hug" or outline your unit. Can sometimes come off as being a bit immodest, so know your audience lol.