When Buying clothes its best to know there size. If you dont this could be bad so its always best to be sure. Another thing about buying clothes is you might pick out something that they personally don't find cool or would like to wear. What i tend to do is find out what stores they like to shop at. This way you can get stuff from that store or get a gift certificate and let them get whatever they want. I think this is the best way because you wont pick something they don't like or wont wear.