I have several different tops for running and these are my first choice every time. I would describe the sizing as a "comfort" fit meaning that it is not tight and the length is good. I have two of these in a size "Small" and one in an "Extra Small". I am a UK size 8-10, bust 34B and usually take a small size in running clothing. The extra small size is a better fit for me however the small size is perfectly fine too, just a little roomier. They are light weight fabric, wick the moisture away very effectively and are super easy to wash and dry. These have been so comfy to wear running through what has been quite a warm summer, I never seem to overheat in these tops unlike some of my other running tops. Would highly recommend.