XS:

Example of Breed: Toy Breeds, Pomeranians, Mini Fox Terriers.

Weight LBS: 6-11.

Neck Inches: 8.5-12.5. 

Girth Inches: 10.5-16.

S:

Example of Breed: Cavalier King Charles, Fox Terriers, Maltese Terriers.

Weight LBS: 11-22.

Neck Inches: 12-19.5. 

Girth Inches: 15-24.

M:

Example of Breed: Cocker Spaniels, Beagles, Kelpies, Miniature Poodles.

Weight LBS: 22-44.

Neck Inches: 14.5-23.5. 

Girth Inches: 17-28.

L:

Example of Breed: Labradors, Border Collies, Boxers, Dalmations.

Weight LBS: 44-77.

Neck Inches: 16-27. 

Girth Inches: 20-33.5.

XL:

Example of Breed: Golden Retrievers, Salukis, German Shepherds.

Weight LBS: 77+.

Neck Inches: 19-32. 

Girth Inches: 23-40.