I think it all depends on the particular dog, the size of its parents/grandparents/etc and size at birth. In my experiences, most seasoned breeders (unless they aren't honest with you) can tell approx. how large a particular puppy will be full grown.
*My Baron has stayed right on track with most of the growth charts I looked up when I got him. At 12 weeks old he was under 1.5lbs and now he's 1 year old and almost 3 lbs. |