My 8-year-old daughter wears a size 8 and the medium fit her perfectly. The quality of the shirt is very nice and my daughter loves that the light sabres glow in the dark. I bought it for her to wear to school on May 4th. Unfortunately, I did not know her class was planning on dressing up in Star Wars gear that day so with only a few days notice, I was worried. I ordered this the night of April 30 and received it during the day May 3! Great service!