I want to buy this knee sleeve but don't know the size (L or M) - link provided?

Don't waste your money, the only knee braces that will doing anything for your leg/knee are big and made of metal, anything else is like a warm hug it's nice, but it doesn't do squat. The best course of action would be to let your knee heal depending on whats wrong with it, if anything. So what problems are you having with your knee, symptoms?