chihuahua question?

i brought an male chihuahua and he was the runt of the litter but no one wanted him and he was there with his brother and the lady took his brother and he was left with a white/ chocolate male, and white and blonde male and a white and blonde female and he was the tinyest one there he looks so cute and he looked like my female that will be a year on mother's day. I was wondering how big will he get cause hes the runt and he only weighs 2.6lbs at 6 months he didn't grow at all. i was just wondering cause i know chihuahua's weigh from 2-6lbs and i also know there are teacups and pocket size and there are normal size chihuahuas. its like he's not going to grow. i mean i don't care if he will be a big chihuahua i will love him no matter what i was just wondering thats all cause i got an female and she is 6lbs and i also have 2 mixes chihuahua/rat terrier and one is only 12lbs and the other one is between 15-35lbs honestly.