Pop in to your local jewellery store and have you finger professionally measured or take a ring that fits your desired finger perfectly and let them measure it for you.
Tip : Finger sizes change as a result of the temperature, fingers are bigger in warmer weather and shrink in colder weather. Measure your fingers at the end of the day and when they are not too cold for the best results.
Another option is to measure an existing ring that fits you well. You do this by measuring the diameter of the ring in millimetres
Step 1: Choose a ring that fits the desired finger
Step 2: Measure the INSIDE diameter in millimetres
Step 3: Use the conversion chart to determine your ring size