There are two ways to find your ring size:
1. Take a ring that fits you and always measure the diameter from the inside of the ring (discarding the thickness of the ring), as shown in the following figure. This measurement in millimetres will be the diameter. Check the size with the following table.
2. Use a string or paper tape to encircle the finger near the knuckle in a tight but not tight way. Make a mark and what you measure up to the mark will be the measurement in millimetres of the length of the ring. Check the size with the following table.
You can then check the size of the necklaces. The centimetres correspond to the length of the chain or cord. These measurements are standard and can vary depending on the person's body.