16 week puppy is undersized Questions

Good Afternoon,

I have a 16 week GSP, born January 27th and he appears very undersized.

1: He seems undersized. I took him to the vet today and he weighed 20 pounds, without breakfast, so maybe he is typically 21 or 22. I have looked at charts online and this seems like it is significantly below the average, is this something to be concerned about? Is there a specific puppy food that would better help growth?

I’m not a fan of puppy/adult weight charts,and they make so many people worry needlessly.
There is no such thing as an ‘average’ puppy because each puppy is different, and grows at different rates.
There are all sorts of things that factor into the eventual size/weight/height, depending on genetics, build, and bone structure etc. A good breeder should be able to give you a better indication as they will know their lines.
As long as he looks healthy I wouldn’t worry.

If the vet was not concerned then just let the puppy develop and grow at his own rate. At 16 weeks he is still very much a baby.