O/S one size fits most. Elastic and adjustable. Faux Leather, Metal ring. Take a measurement tape and your posture should be nice and straight, without holding in or sticking out your stomach, Locate the bones on the right and left side of the abdomen. For Dngeon measure approximately 5 inches under the belly button. Now locate the range between any of the values on the table and that would be your size. Adjustable size. Dngeon One Size. 28 inches to 46 inches. Wide straps on harness on an imitation leather fabric. Completely open back and front.