A pom usually gains their approximate adult size by 4-6 months. That of course does not account for overfeeding. Some breeders have size charts posted on their sites but I cannot vouch for their accuracy.
Yes it can be charted for a rough estimation of it's adult size. Usually at 8 Wks it's weight can be tripled and at 12 weeks doubled. Some variations can occur depending on development diet ex resize and wether the Pom is fixed. But rule of thumb most dogs are not fully finished growing until 1 yr of age. It will continue to fill out with age. Breeding females usually get a tad bit bigger after every litter of puppies. But yes MOST of the growing is done by 6 months, however it is still only 1/2 head old so let's say your Pom at 6 months weighs 5 lbs. at a year it will prob be in the 7 lb range at a year