im not sure how the sizing works

Here is the sizing info from O'Clock's website: SIZE GUIDE / SUGGESTIONS The O'CLOCK watch range comes in 3 sizes (Small, Medium & Large) and should fit most people. It's made of a soft silicon fabrication that easily stretches over you hand and holds it's shape very well. The way it fits you is of a personal preference. Some like it tight and some like it loose ... The measurements we provide is the CIRCUMFERENCE of the internal portion of the watch. The best way to measure your wrist would be to wrap a string of some sort around it and mark it. Then measure the length of that string up until the point where you marked it off. Keep in mind the silicon stretches. THE SIZES MEASURE AS FOLLOWS: SMALL: 6" MEDIUM: 7" LARGE: 7.8" If you are buying it as a gift a guide would be as follows... Small - 150lbs or less* Medium - 150 - 195lbs* Large - 195lbs +* *We obviously cannot guarantee this however! We suggest a wrist measurement.