When your human measures your chest, have them measure right behind your front legs.

 Size Neck Chest
S 9-11" 11-18"
M 11-14" 14-22"
L 14-16" 18-27"
XL 16-18" 23-32"


Collars fit different ranges, with overlap between sizes. If your neck fits two different sizes, pick the collar width that you prefer.

Size Neck Collar Width
Medium 13-20" .78"
 Large 16-26" 1"