I bought two harnesses and both are too big. I measured my dog and according to my measurements a medium should have fit. I have a long haired chihuahua and he weighs 8 1/2 pounds. The part that goes around his girth fits a little loose but the neck is too big and my dog can slip out of it very easily. I don't know if the small would have worked because my Pip's size was bigger than the max size for a small.
I measured my cat multiple times, his chest is 16.5 inches around, and this harness is comedically large on him. I'm going to try ordering the small size instead, despite the measurement differences. Will post again when it arrives to tell you how it fits.
Harness is attractive but seems to be sized oddly. Make sure you measure your animal before ordering. I bought a Large for a 15 pound ShihTzu and it is very snug - almost too small.
Very nice looking and fairly easy to get on an excited little dog.
Vest itself was ok but didn't fit for the size I usually get