You pretty much know what size necklace you want.  But for bracelets and anklets, if you are unsure, below is an example of how to measure.  I also can add extra links just to be safe~

This is the size of the wrist. For me it is 6".

This is approximately the size bracelet I would want, longer if you like it loose.  For me that would be about 7".

 This is the size of the ankle.  For me that is 7 7/8".  Depending on where you want to wear the anklet will depend on the inches.  Add one inch to wear it below the ankle.