Small - Weight: 5-10 lbs. [Examples: Poodle, Rat Terrier, Shih-Tzu]
Medium - Weight: 10-15 lbs. [Examples: Boston Terrier, Cocker Spaniel, Lhasa Apso]
Large - Weight: 15-20 lbs. [Examples: Westie, Corgi, Schnauzer]
X-Large - Weight: 20-40 lbs. [Example: Scottie]
XX-Large - Weight: 40-70 lbs. [Examples: Labrador, Shepherd]
Jumbo - Weight: 70 pounds and up [Example: Basset]