Kitten Size: Less than 6 months old
These fit most kittens by the time they reach the age of 16 weeks. Some kittens can wear them as early as age 12 weeks.
Small: Approximately 6 months old -- Approximately 6-8 pounds
Large kittens at 5 months may need the small size and small-boned adult cats often wear the small size.
Medium: Approximately 9-13 pounds
Most adult average size cats wear medium.
Large: Approximately 14 pounds and up
Large-breed cats wear large.