Ring Size Conversion Chart
We highly recommend you visit a local jeweller and have your finger measured professionally prior to purchase. However if you are happy to measure your finger yourself it can be done by taking a piece of string and wrapping it around the base of the appropriate finger.
Make a mark with a pen at the point the string joins and begins to overlap, and then measure this against a ruler in millimetres. This will provide you with the circumference measurement of this finger.
Please ensure you do not measure your fingers when they are particularly cold as your finger size will be smaller at this point.