Well for starters, Stedman is 4lbs and wears an XS (except for the occasional size S, because some things just run different...I think out of the over 20 outfits that he has, only 2 of them are size S). But he has a really tiny build. He doesn't even look like he weighs 4lbs. My friend has a Yorkie that weighs 4lbs and it looks MUCH bigger than Stedman does. Anyway, if I were you, I too would wait until you get your baby home. You really need to measure them...chest, waist, neck, leg length, body length, etc. to be 100% accurate and make sure you get the right size. They don't always weigh what the breeder predicts them to weigh either. Sometimes they end up being smaller, sometimes bigger...ya just never know
It's impossible to be 100% positive on what they will weigh.