To avoid you to make a mistake in the choice of your bracelet, here is a little guide that will helps you to know the size of your wrist and to make the right choice.
There are many objects and ways to help you to measure your wrist. With a tape measure, a string or a ribbon circle your wrist without tightening too much. The ideal would be to be able to slide a finger under the ribbon.
Write the length you have got after measuring your wrist and add it between 1cm or 2cm. For example, if your wrist measures 18cm, the ideal size to choose for your bracelet is 19cm. It also depends on the ways you want to wear your bracelet. The medium size of the bracelets for a women is 19cm and 21cm for a men.
This is also possible to use one of your bracelets to measure your wrist. For this purpose, take your bracelet and a ruler and measure it from one end to the other including the clasp and the tie.