How to determine your ring size
Wrap a piece of string or a strip of paper around your finger.
Mark the point where the two ends meet.
Measure the string or paper against a ruler to get the circumference of your finger.
Or for the diameter, divide that by 3.14 to get the diameter of your finger.
LETTERS (AU) NUMBERS (US) INNER DIAMETER CIRCUMFERENCE
J, K, L 5 15.7mm 49.3mm
L, M, N 6 16.5mm 51.8mm
N, O, P 7 17.3mm 54.4mm
P, Q, R 8 18.1mm 56.9mm
R, S, T 9 18.9mm 59.5mm
T, U, V 10 19.8mm 62.1mm
V, W, X 11 20.6mm 64.6mm
X, Y, Z 12 21.4mm 67.2mm
Z, Z+1, Z+2 13 22.2mm 69.7mm
Z+2, Z+3, Z+4 14 23.0mm 72.3mm