I think at 6 months it is too hard to determine size (still too young). My vet goes by doubling the 4 month weight and adding a pound, which has been right in my experience. I have a 6 pound Maltese and a 2 pound yorkie. My yorkies size has not been a factor at all. The older dog knows instinctively how rough she can be with him. However, I do sometimes worry about my 2 pound yorkie being too rough with my 6 pound Maltese. How big were your yorkies parents. That should also help determine size. Karen |