In ON THE LOOSE, Thelma Todd also gives her dress size as "36". I believe this is a reference to the ideal of "the perfect 36"*, but that type had been eclipsed by the "flapper" look, which was still considered fashionable in the early thirties. Thelma Todd would not actually have been a size 36 in real life. Possibly she would have been one if not for the dieting that Hollywood was forcing on the actresses, something which they claimed was necessary that was actually unhealthy.
ROUGH SEAS also said Thelma Todd was size 36.
*Something that had been used as the title of a Mabel Normand film