Small

Dimensions: Neck = 8" - 14", Chest = 16" - 26", Back T-Strap = 4"

Medium

Dimensions: Neck = 14" - 25", Chest = 22" - 34", Back T-Strap = 5.75"

Large

Dimensions: Neck = 18" - 37", Chest = 24" - 40", Back T-Strap = 6.25"