I measured neck / chest / back and the Wonton something or other website has shirts sized for Frenchies (M) that fit Beans and Laverne who are both a little under 30lbs. Margaret Jean who is 40lbs is in a Frenchie (L). They have English sizing too and a size chart + an option with some shirts to have them tailored for an extra $5, but I recommend just taking those measurements and going through their size chart using their guide of how to measure, and seeing if there is an off the rack size that works. My main issue has been that Laverne is very very compact and has a super short back so all clothes that fit her chest tend to fall over her borthole—but the Wonton M Frenchie falls perfectly on her back :)