I ordered size SMALL as I'm a size 10 and it's HUGE on me! That's OK as I will be able to wear it during winter with a big winter coat underneath. I got this for cycling to work in busy London traffic. Love the pink colour! For reference I am a size 10, 58kgs, 5 foot 4 with a DD bust and the small is really big. I should have ordered the XS. Oh well, it only cost a few £ and it will serve it's purpose of making me more visible whilst cycling in traffic. It's really thin and light which is what I wanted so I can fold it up really small to keep in my bag when I'm not cycling. If you're wanting something a bit more sturdy, hard wearing and substantial then you should go for something a little more expensive but I think this is fine for what I need it for.