The QRay Bracelet come in three sizes: small, medium, and large. 75% of women typically wear a small size. 75% of men typically wear a medium size. We do offer extra small and extra large in select models. Size small is 6 to 7 inches circumference of your wrist. Size medium is 7 to 7 3/4 inches circumference of your wrist. Size large is above 7 3/4 circumference of your wrist. When ordering from the Official QRay Homepage or the QRay order line and you find that the bracelet size is incorrect, you can send the bracelet back to us for a hassle-free size exchange.