Unfortunately, the size M was way too small for us as well. I was really shocked and could see right away that, in my opinion, it doesn’t match a normal M. Our dog always wears M, and this one is much too small. Such a shame, I really liked it.
I ordered size L for a chest circumference up to 70cm, which should have been just right for our dog, but it couldn't even fit over his head.
Much too small for a size L, I'd actually say this is a size S.