A quick look online lists very small looking measurements - much smaller than either LK Bennet or Coast for example.
I mostly wear a 16, very occasionally a 14 on top, with the odd 18 if a dress is cut tight on the bust.
A Banana Republic dress is a possible contender for a bridesmaid dress for a wedding next summer where I am bridesmaid (one of many) so if there isn't going to be a cat in hell's chance of me getting into one then I need to say so now before multiple dresses are ordered.
I've never bought anything from a BR, and have no idea where my nearest one is. Gah.