Show shirt sizing

I was wondering what size of show shirt I would probably need. I'm a size 2 or 4 (depending on brand) in dresses and a size 2 in show coats. Typically wear a size S in shirts. Would I be a 32, or a 34? If you need to know, I'm 5'4" and probably about 120 lbs. Thanks!

It's generally about one size up from your bra size. So if you're a 34 something? You'd get a 36 show shirt. (except for Tailored Sportsmans. Those come in regular dress sizes) However some brands fit differently. FOr example, IMO Ariats are a lot boxier and roomier then the essexes.