"toy chihuahua" isn't a legitimate term. this is a made up category.
It depends on the size of the parents. I would guess that it was a cross of a Toy Poodle and a Chihuahua, both of which are relatively small, making a Chihuahua-Poodle relatively small (less than 10...
well they grow pretty small i mean my nighber has 2 chihuahuas and one is 9 and hes small
they grow small they grow propeblyas a miniture or toy poodle
They can vary from 2 - 12 pounds but rarely get over 6 pounds. See the related link for more information.
I have a few chihuahuas of my own and they are all teacups. They only weigh two and a half pounds max.