I purchased a 6-9 month for my 5 month old - he's 26 inches long and 17 lbs.  I wanted him to have something on that one no other baby would - and this was it!  It looked great on him.  It's not too breathable so be sure to put this on your baby right before you get up to get his baptism done, unless it's just a colder day.  Great material, pleats were a great touch, I enjoyed the detail and overall the outfit fit perfectly - when he stood up.  when he layed down he liked to kick his feet and the legs on the romper would go up to his calf, but no big deal.  It did the trick.  Awesome product.