Typical adult shirt sizing. Youth M size is the middle ground for youth sizes and I have found that the youth L and XL are very close to the adult S, and the youth S is very close to the youth M. For average builds, I would recomend a youth M for ages 6-9 and an adult small for ages 10-13. Please send me a special request if you need to have a size that is not listed. Thank you!
