How to Know Your Size:

Measure your wrist or ankle with a flexible tape measure. Make sure the tape is snug to your skin when you measure. Add .5 inches to whatever your measurement is and that is your bracelet or anklet size. 

ex: If I measure my wrist to have a circumference of 6.0 inches, then I would choose the 6.5 inches size option.

It all depends on how you prefer your jewelry to fit, these are just tips.