Size Guide

Size	Diameter	Height	Cat weight
S	13.8" (35 cm)	5.1" (13 cm)	up to 9 lbs (4 kg)
M	16.5" (42 cm)	5.5" (14 cm)	up to 18 lbs (8 kg)
L	18.9" (48 cm)	5.9" (15 cm)	up to 22 lbs (10 kg)

Between sizes? Go one size up — cats love room to stretch.