Hi there, 3-4 pounds is fine. I think the average is about 5 pounds though. Yours is on the small side. The standard size for Yorkies is no less than 7 pounds and height between 6-9 inches tall, I would think that is measuring from the toe to the shoulder blade, not his head. My Maximus is 6 months old now and about between 3-5 pounds and 7.5 inches tall.