I started water aerobics a few weeks ago.   Well Monday night I grabbed a blue flotation belt as they are the large size. (they are based on weight and length of the strap not clothing size)  I got back to the pool only to realize it was marked medium.  I started to walk back to exchange it and the instructor asked what was wrong.  I said blue is usually a large this one is a medium.  She said "don't you take a medium?".  It was nice to hear and she doesn't know i had the surgery.  I used the medium without issue!..