I needed an elastic strap for my 4 year old to help him get his large pants up and down quickly. The instructions say to order the belt the same size as his waist, so I ordered a size 21. When it arrived and tried it on my son, the belt was exactly the same size as his waist! If I wanted it to fit properly I would have to pull it too tight and tie it around his waist, defeating my purpose. So I returned it. However, as I like the style of the belt and the fact that it stretches, I just ordered it up a size.