around the neck or top is 4 inch across, the girth (adjustable) goes from 4 inches to 6 inches. length in 5 inches. my dog is a miniature daschaund and he used it at 7 weeks old just when we traveled and he is now 16 weeks old. his head is to big to comfortably fit through the top.
depends on how big his head and ears are... lol my pup is almost albs and his head and ears are just a little to big for it to go on comfortably. otherwise it fits him perfect. hope that helps.
Unfortunately I do not know anyone who owns a little guy like him or I would go try it on them . . . but I think since he is done growing, you won't run into the problem I did with mine filling out. He is still young and fluffy :) If you are near a pet store, maybe take him in and try one (xsmall) on. Thankfully this one is free and ships free, so the most you loose is credits that if it didn't fit, you could repost and probably make the credits bake. Win - win for you :) Otherwise, if you won and it didn't fit, we could work that out. I'm pretty easy to get along with and I know it's hard to not have it in hand to try on and help make the decision.