In order to know your bracelet size, the easiest way I have found is to use a piece of string and measure at a comfortable point where you would like your bracelet to sit. Measure the length of string and this should do it.
Please remember to add just a touch of length to the string so the bracelet isn't too tight. There is also confusion of size versus length. Size, which is listed for most bracelets, refer to the inner diameter of a bracelet which is a more accurate reading. Length is just the measurement from one end to the other.