I didn't buy anything smaller than 000, because I expected to have a big baby, and figures that if I need smaller, I can go out and get them, but if I buy them and they're too small, I cant use them at all (since I pre-washed them all, so no returning)

Milo was about 10lb 3oz/4.6kg, and he just fit 0000 for about a week, but 000 were fine and not overly big so he mostly wore those.