There are simple ways to check your size for bracelets.
Take a piece of string and wrap it snugly around your wrist where you want the bracelet to sit. Mark the place where the ends meet. Stretch the cord out alongside a ruler to measure it; and then, the important bit - add 2cm to the length.
On our chart below, pick the size closest to your measurement. If you are between sizes, consider how you wear bracelets - do you prefer a relaxed fit or something tighter? This will help you pick a perfectly-sized piece.