You may have heard the word teacup and Chihuahua used together. It may surprise a lot of people that there is no such thing as a teacup Chihuahua. Now I am not disputing that for a couple of weeks of life most Chihuahuas will fit into a teacup. I am not disputing that there are tiny Chihuahuas either. There are tiny ones. I have seen them myself. I had two who as adults weighed only three pounds. One of them was four months old and only weighed a half a pound and at a year old was only a pound. By three he weighed three pounds. I had one girl who weighed six pounds most of her life but after age five she put on some weight and ended up weighing ten pounds. She was what the vet called a hardier Chihuahua and the vet didn't feel she was over weight.
To a reputable Chihuahua breeder there is no such thing as teacup Chihuahuas. I know one breeder who if you use that word with her you will get a quick lesson in Chihuahua. She takes offense to that term used with the Chihuahua. Elizabeth was just weighed and she weighs six pounds and is seven years old.
At times a breeder may have a teeny tiny Chihuahua. The majority of those teeny tiny Chihuahuas are in actuality runts of the litter. It happens especially in a large litter. Reputable Chi breeders won't breed for that tiny size. In fact breeding a Chihuahua is really risky. I guess that is where I probably need to stop this post so that it doesn't turn into a post about breeding them when this post is about those called, The Teacup!