It's been around for ages. It's not exact but it does give you a reference. Check the weight of your pup against its age, scroll down & you can get an estimate of its adult size.
Example: 8 wks/13 oz = 2 1/2 lb adult
AKC Inspected January 2019
Uniting families together one Chihuahua at a time.
Salem's Finest AKC Chihuahuas
"We don't just sell puppies to people; We choose our puppy parents to be part of our extended SFC family for a lifetime."