So by the look of the picture I went with medium assuming it ran a little small. The material is great, slightly stretchy if you need it to be and the bottoms cover the majority of my butt. I'm 5"5', about 120 lbs. The bottoms for great, never had a problem down water slides or anything. I'm an A cup so the top were a tiny bit lose especially towards the bottom but once they're wet it clings so nothing is exposed. When I jumped in the water though the top flew up and the pads were easily messed up. Not a big deal though overall it was a great purchase I recommend it!