I originally bought a 120 size (aka M) for my 11 year old daughter who wears a size 10. The 120 size was way too small. Then we returned this and purchased a size 140 (aka XL). The 140 fits my daughter who is a slender gymnast like a glove. I don't think it will fit her in 4-6 months as she grows. It is perfect for this Halloween and she loves it. It looks great. As a mom, I wish I would have bought one size bigger so she could wear it for dress ups this year or a back up costume again next Halloween. It's a great costume just buy many sizes up. It's a slim fit.So when I say Lucky I mean that thank goodness my kid was able to fit in it.. she is a tall petite 7yr old. The dress doesn't have a zipper it's slip on dress for anyone wondering.I ordered my daughter an extra large (150) being that she's a size 10-12 in girls. I received a large (140) which was too small. Luckily I had enough time to reorder the xl, crossing my fingers it fits. Manufacturer sent me the wrong size. Material is very thin, easy to snag and cheaply made. Don't expect more than one use from this item. Good luck.Perfect for my 5year old, fit like a glove, a tiny bit snug - worked fine just means we definitely won’t get another year out of it ! She loved it!do not fit a 12 year old. for a very skinny and short child, material very cheap.My daughter had this on legit enough time to ride in the car and arrive at a Halloween party and her dress ripped. Before we even had a chance to trick or treat. I wouldn’t buy this item. Super cheap.Had to order a Xl for my child who normally wears a child’s size 8. Was still snug. The fabric ran and was ripping in the first hour.This did not hold up and was not true to size at all