I agree with previous posters: these run SMALL.  It probably doesn't help that my 2 month old is a bit over 15 pounds and 24 1/2 inches long, but I hoped the 6-9 month size would fit him for a while...NOT without me stretching the onesies out after washing them, and air drying them. Good thing I only bought 1 pack, because that's a lot of trouble to go through to launder baby clothes (I'm only doing it because I'm stubborn about wasting money, so I want to get a little use out of these!).

Sure do wish more newborn clothes came with the built in mittens, which is why I bought this item in the first place...