There is no way to tell how big your dog will be when it is full grown, honestly. People can estimate, but there's no magic formula. Like children and teenagers going through growth spurts at different times, so do dogs. By the time your dog is about 10 months old, it will be done with about 85 to 95 percent of it's growing... in general. That's why it's so important for people not to buy 'teacup' dogs. You have no idea if athat so called teacup puppy is going to stay tiny or turn into a giant of the breed. The size of your pomeranian seems to be a pretty big concern to you, may I ask why you are worried about her growth?
In general - you can triple a puppy's weight at 8wks, and double a puppy's weight at 12 wks to get somewhat of a close estimate to how much it will weigh as an adult. This type of estimation tends to get you into the general ballpark, but as with anything, there can be variations -