I wear an American size 31 Waist and I originally bought a size medium but they were too big. I next ordered size small, but the waist was still loose and they were sliding down.
They look great and are very comfortable. Almost like sweat pants. Just make sure you know that these pants have no way to adjust the waist other than the elastic built in. I didn't have time, but if I would have added strips of elastic as suspenders, they would have been perfect.