XS - Kitten : (less than 6 months old about 5 pounds / 2.5 kg)
Soft Cat Nail Caps will fit most kittens by the time they reach the age of 16 weeks (4 months). Some kittens can wear them as early as age 12 weeks (3 months). To test, try a nail cap on first without the adhesive. If it looks too big, don't glue it on. The nail cap should fit snugly, like a glove. To accommodate younger kittens, you can trim the base of the nail cap making it smaller so it will fit your kitten's nail. Kittens up to about 5 pounds / 2.5kg and/or 5 months generally fit the kitten size.
S - Small : (approximately 6 months old-approximately 6-8 pounds 2.5-4 kg)
Some kittens at 5 months may need the small size if they are growing fast or are large-breed cats. Small-boned adult cats often wear the small size. If your cat seems smaller than an average full-grown cat, choose small.
M - Medium : (approximately 9-13 pounds 4-6 kg)
Most adult average size cats wear medium.
L - Large : (approximately 14 pounds 6kg and up )
Very large-boned and large-breed cats wear large. Maine Coons, for example, are very large cats and generally wear large.