The Hayabusa Performance Rashguard sleeves are designed to be a full length "one size fits most." It is designed to be formfitting so it stretches, and uses compression to help keep your arms warmed up & loose. The circumference for sleeves are more important in determining what size to get. The average circumference can be from 9" in the forearm area up to 12" in the bicep area. Please remember that the sleeve stretches to fit arms slightly bigger than the measurements below. S/M - 9" - 11" L/XL - 11"-13"
Answered on 4/1/2013 by Javi the MMA Guy from Wheeling, IL