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Ring Size

UK size
US size
Inside diameter
(mm)
Inside circumference
(mm)
A
1/2
12.04
37.8
B
1
12.45
39.1
C
1 - 1/2
12.85
40.4
D
2
13.26
41.7
E
2 - 1/2 13.67 42.9
F
3 14.07 44.2
G
3 - 1/2 14.48 45.5
H
4 14.88 46.8
I
4 - 1/2 15.29 48
J
4 - 3/4 15.49 48.7
K
5 - 1/4 15.9 50
L
5 - 3/4 16.31 51.2
M
6 - 1/4 16.71 52.5
N
6 - 3/4 17.12 53.8
O
7 - 1/4 17.12 55.1
P
7 - 3/4 17.93 56.3
Q
8 - 1/4 18.34 57.6
R
8 - 3/4 18.75 58.9
S
9 - 1/4 19.15 60.2
T
9 - 3/4 19.56 61.4
U
10 - 1/4 19.96 62.7
V
10 - 3/4 20.37 64
W
11 - 1/4 20.78 65.3
X
11 - 3/4 21.18 66.6
Y
12 - 1/4 21.59 67.8
Z
12 - 1/2 21.79 68.5