What is the full size of a Yorkie terrier? My two puppy are 8 months and they weight 5 pounds?

they are probably about the right size for their age. Should be about 7 lb grown which is within the standard.
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i dont think they are going to get much bigger, maybe 6 pounds max.
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It sounds to me like they're full grown. Yorkies are tiny.

Here is a good Web site for Yorkie info:

http://www.dogbreedinfo.com/yorkshireterrier.htm
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No more than 7 lbs, thay are smaller dogs.
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They are probably reaching maxim-mum. Usually they will be up to 5-7 and a half lbs.
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Some Yorkies can go up to 7-10 lbs, but most won't go past 7. Yours sound like they're pretty much done all their growing!
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Assorted websites.

they won't get much larger. most dogs stop growing at around 6-9 months old, so they will either get a little bigger, or they are done growing.
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I think they r overweight. A puppy 8 months should weigh like 3-4 pounds!!!!!!
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MY BRAIN

My yorkie stopped growing at about 7 to 8 months old. He was about 6lbs. But then he lost a bit of his baby/puppy weight. He was 5.4lbs at his last vet visit at two years old.

But his father was 4lbs and mother was 7lbs.
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The size of the parents is only part of the equation–the size of the other dogs in the bloodline also attribute to the size of offspring. The standard for the Yorkshire Terrier calls for them "not to exceed 7 pounds." Your little ones will continue to grow until they are around 1 year old…they will likely come close to the 7 lb mark, maybe a little under or over.
Unfortunately, the definition of the Yorkie as the standard defines it means little these days. There are too many unethical breeders producing dogs with no consideration of the breed standard, so you have dogs with sizes all over the scale.
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Yorkie breeder 10+ years