Good question! I just checked out one of my cats that is 10lbs. I believe it would fit. It is impossible for me to try it on her though, she wouldn't give me the chance.
Lol,my cat only wears it when we take him outside other than that he hates it. I'll be watching and if it doesn't get to high I'll be bidding, spent most of my credits at the beginning of the week lol
i have a 11 lb chihuahua and he has same harness and he wears a large..and it also adjusts bigger incase he gets a lil bigger..lol..i also have the matching leash and collar...they are cute..
the small one will definately not fit a 10 lb or larger animal...you need the size large for 10lbs or more...the large will probably fit up to a 12 lb dog. or cat.