Measure the exact size of your wrist in the place where you would normally wear your bracelet.

Use a flexible measuring tape (like the ones from IKEA or a sewing store)

or

Wrap a piece of string around your wrist and mark it where it overlaps. Then place it on a flat surface beside a ruler.

then

choose how tightly you want your bracelet to fit, for example:

if your wrist size is 6″

A 6″ bracelet would be a snug fit

A 6.25″ bracelet would be a comfortable fit

A 6.5″ bracelet would be a loose fit

If you need more assistance