Below is a chart that shows some basic guidelines to bracelet sizes for men, women and children. These measurements are approximate.

How to measure your wrist:

Use a seamstress measuring tape (the soft and flexible type), and wrap it around your wrist, about where you want the bracelet to sit.  You have your wrist measurement in cm.

or

Use a strip of paper and wrap it around your wrist, about where you want the bracelet to sit.  Mark the strip of paper where the the start to overlap, and measure on a ruler or measuring tape.  You have your wrist measurement in cm.

Add the measurement in this table to your wrist measurement, according to how snug or loose you want your bracelet to sit.  It is very important to keep the design and purpose of the bracelet in mind.  For example, Anklets and charm bracelets are usually towards the comfort to loose fitting side, whereas men's leather cuff bracelets are usually worn more snug.

Add this amount where applicable, depending on the style of the bracelet you are buying, and how you want to wear it:

Bracelet size chart