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Global Ring Size Guide

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Lesson 1: A Journey Through the World of Jewellery
Lesson 2: Jewellery's Dual Role: Function and Adornment Through Time
Lesson 3: The Secret Language of Jewellery
Lesson 4: From Nature to Craftsmanship: Materials in Jewellery
Lesson 5: Between Innovation and Illusion
Lesson 6: Alloys and Metal Standards
Lesson 7: Combinations and Colours of Precious Metals
Lesson 8: Laws and Regulations
Lesson 9: Hallmarks and Regulatory Laws
Lesson 10: Authenticity, Fakes and Forgeries
Lesson 11: Precious Gems and Their Significance
Lesson 12: The Shaping of Style: Makers, Patrons and Time
Lesson 13: Forces that Shaped Jewellery
Lesson 14: Jewellery Through the Ages: A Journey in Style
Lesson 15: Global Ring Size Guide
Lesson 16: The Adin Jewellery Glossary

The Measure of Fit: A Global Guide to Ring Sizes

Across the world, ring sizes follow different local conventions, yet each aims at the same goal, a comfortable and secure fit. What reads as L in Great Britain might be 6 in the United States or 12 in Japan, while the ISO standard expresses the same fit in millimetres. At Adin we translate between these systems with care, so that the number or letter you know becomes the size you need.

Regional Systems of Measurement

United States and Canada – use a numerical scale with quarter and half sizes. Each full step adds about 0.8 mm to the inner diameter, or roughly 2.5 mm to the inner circumference.

Continental Europe – measures by inner circumference in millimetres, usually rounded to whole or half sizes.

Ireland, the United Kingdom and Australia – follow an alphabetical sequence from A onwards, also with half steps.

Japan – uses a whole-number system that differs slightly from the European scale.

Switzerland – adopts a variant of the European circumference system but includes finer quarter-size divisions.

Germany – traditionally measures by inner diameter in millimetres, aligning closely with the ISO standard.

ISO Standard (ISO 8653) – defines ring size strictly by the inner circumference in millimetres and serves as the international reference for professional measurement.

Finding Your Perfect Fit

At Adin Fine Antique & Vintage Jewellery, each ring is carefully measured and recorded according to the relevant standards, ensuring a reliable match between jewel and wearer. Should you be uncertain about your size, our team will gladly assist you in determining the perfect fit – whether through professional measurement in our atelier or guided advice from afar.

For a step-by-step explanation of how to measure your own ring size, , see our seperate guide.

Between precision and poetry lies the secret of every perfect fit — a circle of gold measured not only in millimetres, but in meaning.

Great Britain Europe Japan USA diameter mm circumf. mm
      0 11.54 36.25
a       11.90 37.38
    0   12.00 37.70
a½       12.10 38.01
b       12.30 38.64
      1 12.37 38.86
b½       12.50 39.27
      1¼ 12.58 39.52
c       12.70 39.90
  0.15   1½ 12.78 40.15
c½ 0.53     12.90 40.53
  0.84 1 1¾ 13.00 40.84
  1.00     13.05 41.00
d 1.15     13.10 41.15
  1.50   2 13.21 41.50
Great Britain Europe Japan USA diameter mm circumf. mm
d½ 1.78     13.30 41.78
  1.88 2   13.33 41.88
  2.00     13.37 42.00
  2.13   2¼ 13.41 42.13
e 2.41     13.50 42.41
  2.76   2½ 13.61 42.76
  2.91 3   13.66 42.91
e½ 3.00     13.69 43.00
  3.42   2¾ 13.82 43.42
f 3.67     13.90 43.67
  3.98 4   14.00 43.98
  4.00     14.01 44.00
  4.14   3 14.05 44.14
f½ 4.30     14.10 44.30
  4.74   3¼ 14.24 44.74
Great Britain Europe Japan USA diameter mm circumf. mm
g 4.92     14.30 44.92
  5.00     14.32 45.00
  5.02 5   14.33 45.02
  5.40   3½ 14.45 45.40
g½ 5.55     14.50 45.55
  6.00     14.64 46.00
  6.02   3¾ 14.65 46.02
  6.06 6   14.66 46.06
h 6.18     14.70 46.18
  6.68   4 14.86 46.68
h½ 6.81     14.90 46.81
  7.00     14.96 47.00
  7.12 7   15.00 47.12
  7.34   4¼ 15.07 47.34
i 7.44     15.10 47.44
Great Britain Europe Japan USA diameter mm circumf. mm
  7.97   4½ 15.27 47.97
  8.00     15.28 48.00
i½ 8.07     15.30 48.07
  8.16 8   15.33 48.16
  8.63   4¾ 15.48 48.63
j 8.69     15.50 48.69
  9.00     15.60 49.00
  9.20 9   15.66 49.20
j½ 9.32   5 15.70 49.32
k 9.95   5¼ 15.90 49.95
  10.00     15.92 50.00
  10.27 10   16.00 50.27
k½ 10.58   5½ 16.10 50.58
  11.00     16.23 51.00
l 11.24   5¾ 16.31 51.24
Great Britain Europe Japan USA diameter mm circumf. mm
  11.30 11   16.33 51.30
l½ 11.87   6 16.51 51.87
  12.00     16.55 52.00
  12.34 12   16.66 52.34
m 12.46     16.70 52.46
  12.56   6¼ 16.73 52.56
  13.00     16.87 53.00
m½ 13.09     16.90 53.09
  13.16   6½ 16.92 53.16
  13.41 13   17.00 53.41
n 13.72     17.10 53.72
  13.85   6¾ 17.14 53.85
  14.00     17.19 54.00
n½ 14.35     17.30 54.35
  14.44 14   17.33 54.44
Great Britain Europe Japan USA diameter mm circumf. mm
  14.51   7 17.35 54.51
o 14.98     17.50 54.98
  15.00   7¼ 17.56 55.00
  15.48 15   17.66 55.48
o½ 15.61     17.70 55.61
  15.76   7½ 17¾ 55.76
  16.00     17.83 56.00
p 16.23     17.90 56.23
  16.45   7¾ 17.97 56.45
  16.55 16   18.00 56.55
p½ 16.86     18.10 56.86
  17.00     18.14 57.00
  17.15   8 18.19 57.15
q 17.49     18.30 57.49
  17.59 17   18.33 57.59
Great Britain Europe Japan USA diameter mm circumf. mm
  17.77   8¼ 18.39 57.77
  18.00     18.46 58.00
q½ 18.12     18.50 58.12
  18.40   8½ 18.59 58.40
  18.62 18   18.66 58.62
r 18.75     18.70 85.75
  19.00   8¾ 18.78 59.00
r½ 19.38     18.90 59.38
  19.66   9 18.99 59.66
  19.69 19   19.00 59.69
s 20.00     19.10 60.00
  20.38   9¼ 19.22 60.38
s½ 20.63     19.30 60.63
  20.73 20   19.33 60.73
  20.98   9½ 19.41 60.98
Great Britain Europe Japan USA diameter mm circumf. mm
  21.00     19.42 61.00
t 21.26     19.50 61.26
  21.67   9¾ 19.63 61.67
  21.76 21   19.66 61.76
t½ 21.89     19.70 61.89
  22.00     19.74 62.00
  22.33   10 19.84 62.33
u 22.52     19.90 62.52
  22.83 22   20.00 62.83
  23.00   10¼ 20.05 63.00
u½ 23.15     20.10 63.15
  23.59   10½ 20.24 63.59
v 23.77     20.30 63.77
  23.87 23   20.33 63.87
  23.99     20.37 63.99
Great Britain Europe Japan USA diameter mm circumf. mm
  24.28   10¾ 20.46 64.28
v½ 24.40     20.50 64.40
  24.91 24   20.66 64.91
  24.97   11 20.68 64.97
w 25.00     20.69 65.00
  25.60   11¼ 20.88 65.60
w½ 25.66     20.90 65.66
  25.97 25   21.00 65.97
  26.00     21.01 66.00
  26.22   11½ 21.08 66.22
x 26.29     21.10 66.29
x½ 26.92   10¾ 21.30 66.92
  27.01 26   21.33 67.01
y 27.51   12 21.49 67.51
  28.02     21.65 68.02
Great Britain Europe Japan USA diameter mm circumf. mm
  28.05 27   21.66 68.05
y½ 28.20   12¼ 21.71 68.20
z 28.77   12½ 21.89 68.77
  28.99     21.96 68.99
  29.12 28   22.00 69.12
z½ 29.43     22.10 69.43
  29.49   12¾ 22.12 69.49
z+1 29.99     22.28 69.99
  30.15 29 13 22.33 70.15
z+1½ 30.69     22.50 70.69
  30.81   13¼ 22.54 70.81
  31.00     22.60 71.00
  31.19 30   22.66 71.19
z+2 31.31     22.70 71.31
  31.47   13½ 22¾ 71.47
Great Britain Europe Japan USA diameter mm circumf. mm
z+2½ 32.01   13¾ 22.92 72.01
  32.26 31   23.00 72.26
z+3 32.57     23.10 72.57
  32.76   14 23.16 72.76
  33.01     23.24 73.01
z+3½ 33.20     23.30 73.20
  33.32     23.34 73.32
  33.29 32   23.33 73.29
  33.42   14¼ 23.37 73.42
z+4 33.83     23.50 73.83
  33.98   14½ 23.55 73.98
  34.33 33   23.66 74.33
z+4½ 34.46     23.70 74.46
  34.71   14¾ 23.78 74.71
  34.99     23.87 74.99
Great Britain Europe Japan USA diameter mm circumf. mm
z+5 35.08     23.90 75.08
  35.40 34 15 24.00 75.40
z+5½ 35.71     24.10 75.71
  36.00   15¼ 24.19 76.00
z+6 36.34     24.30 76.34
  36.43 35   24.33 76.43
  36.69   15½ 24.41 76.69
z+6½ 37.00     24.51 77.00
  37.31   15¾ 24.61 77.31
  37.47 36   24.66 77.47
z+7 37.60     24.70 77.60
  38.00   16 24.83 78.00
z+7½ 38.23     24.90 78.23
  38.54 37 16¼ 25.00 78.54