To find the right ring size for you, simply measure the inside diameter of an existing fitting ring and check the measurement against the chart below. Alternatively, wrap a piece of loose string around your finger, being sure to allow for the size of your knuckle. With a pen, mark the point on the string where the end meets, then use a ruler to measure the circumference of your finger, check this measurement against the chart below. (Note: if you are in between two sizes, it is best to size up rather than down).
Ring Size : Inside Diameter : Inside Circumference
I : 15.29mm : 48mm
J : 15.49mm : 48.7mm
K : 15.9mm : 50mm
L : 16.31mm : 51.2mm
M : 16.71mm : 52.5mm
N : 17.12mm : 53.8mm
O : 17.53mm : 55.1mm
P : 17.93mm : 56.3mm
Q : 18.34mm : 57.6mm
R : 18.75mm : 58.9mm
S : 19.15mm : 60.2mm