Just like it is for rings it is the inner measurements that counts when sizing bracelets. And as for necklaces it is a persons preferences and outfit that counts for finding a bracelet's appropriate length.
The bracelet diameter should be a bit bigger than the width of the wrist so that the bracelet will not press the wrist when the hand moves. Too small size squeezes the wrist and wears out the bracelet. Too big size makes the bracelet fall off from the hand.
Ways to find the correct bracelet size:
Measure the circumference of you wrist Use a measuring tape where the wrist is the widest. If you don't have a measuring tape you can wrap a cord / paper shred around your wrist as a bracelet so that it feels comfortable. Mark the point and measure the length. Add a couple of centimetres (a small inch) to the measurement. Correctly sized bracelet leaves some space for the wrist without sticking to the skin.
Measure an existing nicely fitting bracelet:
Bangles and cuff bracelets are sized using the inner diameter or circumference. Multiply the diameter with 3.14 to get the circumference.
Thin chains and chain-like bracelets can be sized by measuring the length, including the clasp if any.
Wrapping bracelets are sized by measuring the length. The amount of wraps gives an approximately diameter/circumference of the bracelet.
Bracelets with large beads and thick/large chain bracelet are always sized using the inner circumference.
