1 - Cut a string about 100mm long.
2 - Wrap around the base of your finger so it fits well but is not too tight. 
3 - Mark the point on the string where it overlaps, forming a circle.
4 - Compare the length of the string to the chart attached.

*If you are between sizes, order a larger size. Make sure your finger is at a normal body temperature (fingers shrink or expand when hot or cold). If your knuckle is much larger than your finger’s base, take two separate measurements and choose a size in between. You want a ring to fit over your knuckle but not be too loose, or it will move around.