My nikko was 2lbs. 4 oz. at 12 weeks. the vet stated he should be 4 1/2 to 5 pounds full grown. He is about 5 1/2 months now and he is 4lbs 6oz, he is changing colors, becoming more steel blue and silvery on his back and nape, and prominent distinction fromm areas that are tan. .the vet says now he should be about 7 lbs. So much for his reliability, I could have made similar predictions and this is my first yorkie. His mother and father are 51/2 and 6 pounds respectively. I know one of his older sisters and she's 5lbs- 2 yrs old, his male sibling from this liter is 2lbs. I think he is still growing and will probably be about 6 1/2 pounds or more. I don't think there is an exact science to weight, it all depends on what you feed them, including treats. Nikko sometimes sneaks food from Qball, which is my Beagle, but he gets plenty of exercise. I must admit, I love him but was hoping he would remain under 5lbs, but I bet my hubby was hoping I remained at 130lbs also. , LOL