Mendota's new line of Small Pet Harnesses - Available in 5 sizes and 4 colors to start out with. Great for our small dog friends, but not limited to cats, rabbits, guinea pigs, ferrets and iguanas! X-Small: 6in to 10in - Small: 9in to 13in Medium: 12in to 16in - Large: 15in to 19in X-Large: 18in to 22in Determine size by measuring pet's torso circumference behind front legs.