When measuring your wrist, stay as close to your hand as possible, like so
(the circumference in the video is 7.25 inches / 18.4 centimeters.)
Don't have a measuring tape?
Use a piece of string to measure your wrist and lay the string back out on a ruler to get your measurement in inches or centimeters.
Please specify the exact number on the measuring tape and whether you prefer your bracelet a little looser or tighter.