Our favourite way of finding your ring size is by measuring a ring that already fits the same finger that you're wanting your new ring for.  Measure the inside diameter of the ring against a ruler and match to the size chart below.
Australian Ring Sizing
Can't Find Your Size? 
Check the below table. 

A 0.5 12mm 37mm
B 1 12.5mm 39mm
C 1.5 12.75mm 40mm
D 2 13.25mm 41mm
E 2.5 13.75mm 43mm
F 3 14mm 44mm
G 3.5 14.5mm 45mm
H 4 14.75mm 46mm
I 4.5 15.25mm 48mm
J 5 15.75mm 49mm
K 5.5 16mm 50mm
L 5.75 16.25mm 51mm
M 6.25 16.75mm 52mm
N 6.75 17mm 53mm
O 7.25 17.5mm 55mm
P 7.75 17.75mm 56mm
Q 8.25 18.25mm 57mm
R 8.75 18.75mm 59mm
S 9.25 19mm 60mm
T 9.75 19.5mm 61mm
U 10.25 19.75mm 62mm
V 10.75 20.25mm 64mm
W 11.25 20.75mm 65mm
X 11.75 21mm 66mm
Y 12.25 21.5mm 67mm
Z 12.75 21.75mm 68mm