The simplest way of determining your finger size is to visit your local jeweler.
However in the event that is not possible please use the following instructions.
1. Take a piece of string and place it around your finger.
2. Hold the position that fits comfortable around your finger with your other hand
3. Then place the string along side a millimeter ruler to measure the length.
4. Use the chart below to calculate your size.
Tips
Perform the above operation when your finger is at its largest, in the evening
Your finger is at its smallest in the morning when your finger is cold.
Buying a ring as a surprise
Find out the ring size from your partners friend or mother.
Alternatively borrow your partners ring and measure the circumference with string.