On the chihuahua growth chart, he's sounds like hes going to be around 6lbs.
Chihuahua Puppy Growth Chart
But its not always accurate, my girl was to be to be 6lbs and ended up being almost 4lbs.
Her birth weight was 5oz., 11w - 2.2lbs, 14w - 2.7, 15m - 3.8, at 2y shes balances at almost 4lbs. Her brother, same birth weight, was 7lbs.