The Rugby Shirts come in chest sizes, by inches, not Sm, Med, L XL etc. To order you will need to know your chest size. The easiest way is to find a shirt which is a comfortable fit, lay it flat on a table and then measure from underarm to underarm, then double that measurement. If you order a shirt from us in size 50″, then using this method it will measure 25″ across when laid flat, so an exact 50″ chest.