Sizing
Rings To make sure a ring will fit you, measure the finger you want to wear the ring on. Take a 5mm wide strip of paper, wrap it around your finger comfortably, mark where it overlaps, remove it and measure the paper length in mm. This is the internal circumference.
The internal diameter is the measurement across the inside of the ring:
Use the table to find your corresponding ring size:

Bangles You can measure your wrist for a bangle in the same way - making the paper circle big enough to get it on your wrist, but not so big that it slips off.