Here are a few pictures of the harness.
This is a size Medium and fits Brawt well and he averages about 17-19lbs. The chest straps are as small as possible and the belly strap is as large as possible. He does have a BIG chest as well.
Charlie (modeling) can slip out of this without any issue. It's too big for him and he averages about 12-14lbs.
Kai (9.4 lbs) wears a size small it's a perfect fit. Nomi (6-7lbs) wears a XS and it is a perfect fit as well.
If you need measurements or anything else let me know. Also, if Petco is sold of them you can order them from www.allthingsjeep.com. I'm going to have to order one for Charlie from there if I can't find one this week. I can't have an odd dog out (even if he really is odd).