Small: Mouth Circumference 4"-5.9", Reference weight 3-5lb.
Medium: Mouth Circumference 5"-7.8", Reference weight 5-9lb.
Large: Mouth Circumference 7"-9", Reference weight 11-18lb.
X-Large: Mouth Circumference 8"-11", Reference weight 19-26lb.
XX-Large: Mouth Circumference 11"-13", Reference weight 26-79lb.
Reference weight and recommended breeds are for reference only, Please refer to the size of the mouth circumference