I have a 22" waist, so I've actually had trouble find something to wear as a back brace for work. I really don't think the small would fit anyone larger than me. It doesn't overlap very much on me, and I don't even have to pull the elastic parts all the way together to get a nice snug fit. A medium would probably even work for me. It would be a good idea to go up a size or two. I'm actually below the lower limit on the small and I maybe could have gone up a size.

It would definitely be visible under normal clothes, so that's something to consider depending on your needs. I wear it over a tank top, with my uniform shirt over it. Seems like good quality, I would order it again if I manage to wear this one out.