There are a number of ways to measure your ring size. The most accurate method is to visit your local jeweler and have your measurements taken.
If you are not able to do this, it is best to use a suitable ring to determine the ring size, you can do this as follows:
You have a ring that fits: Place the ring along a ruler and measure the diameter of the inside of the ring. The number of millimeters of the ring is also your European ring size.
Can't wait? Then take a strip of paper or string and wrap it tightly around your finger, but make sure that the strip or string still fits over the knuckle of your finger! Mark the place where the paper or string meets and measure the distance with a ruler (mm). This gives you the circumference of your finger, on the basis of the table below you can read the European size.