Ring Sizer
1 Find a piece of non-stretchy string about 6" long, or a strip of paper about 6" long and 1/4" wide.
2 Wrap it snugly around the base of your finger.
3 Using a pen, mark the point on the string or paper where it overlaps, forming a complete circle.
4 Measure the string or paper against a ruler to get the circumference of your finger.
5 Divide that by 3.14 to get the diameter of your finger. (Note that you can also use the measurement found in the step above in the form below by selecting it as the Circum (mm).
6 Look up your ring size using the form below.

Variations in temperature can affect the size. Cold causes the finger to shrink, while heat makes the finger expand. Measure your finger in warm temperatures at the end of the day.

If you are buying the ring as a surprise:
Ask your intended recipient’s mother or friend if they know his/her finger size;
Borrow one of your intended recipient’s rings to find their ring size (Make sure to borrow a ring that fits the finger you intend your gift ring to fit.)