If you are unsure about your ring size, it's easy to measure it!
Cut a very thin piece of paper and wrap it around your finger. Make sure the paper is below the joint of your finger and closest to your knuckle. Also ensure that the paper is comfortably tight around your finger for an accurate measurement.
Mark the spot where the paper meets and measure the distance between the two points with a ruler. This is the circumference.
Use the chart below or the sizing tab in the product page of the ring you desire to determine the correct size for you.