Step 1: Measure around the circumference at the Stoma or around the waist area. Step 2: After you have accurately measured for your product size, click on the appropriate product in the size chart below. Tips for after you have your Waterproof Ostomy Protector Stretch the waterproof ostomy protector over the ostomy or stoma until the site is completely covered, with at least an additional inch on either side. The top and bottom opening should be smooth and snug against the skin. If you need help determining what model will work best for you or need help in ordering, please do not hesitate to contact our professional staff by phone 1-888-337-9776. Waterproof Ostomy Protector Size Chart Ostomy Protector Model # Circumference Extra Small OS-12 26- 30 inches Small OS-14 30 – 34 inches Medium OS-16 34 – 38 inches Large OS-18 38 – 42 inches Extra Large OS-20 42 – 46+ inches