mm to Ring Size Converter

Created by Kenneth Alambra
Reviewed by Komal Rafay
Last updated: Jun 05, 2023


If you're finding a way to convert the circumference or diameter of a finger in millimeters to its corresponding ring size, then this mm-to-ring size converter is for you. With this calculator, you can find the correct ring size by measuring the length of a string or a strip of paper you can wrap around any of your fingers.

In this calculator, you will learn the following:

  • How to find your ring size using this mm-to-ring size converter;
  • How to determine the ring size using the mm-to-ring size chart; and
  • Some frequently asked questions about the conversion from mm to ring size.

Keep on reading to start discovering your fingers' ring sizes. ๐Ÿ’

How to find your ring size using this mm-to-ring size converter

You can easily determine your ring size by wrapping the knuckle of your finger using a non-stretchable string or a strip of paper and marking where one of its ends falls, as shown in the image below:

Illustration of how to measure a finger using a strip of paper and a ruler.

With a ruler, measure the length of that string or paper in millimeters and select the closest value available in the drop-down list of our mm-to-ring size converter's Inside circumference variable.

Our tool will display its corresponding US & Canada ring size and other equivalent ring sizes (used in UK & Australia, France & Russia, Germany, Switzerland, or Japan) if applicable.

If you want to find the ring size of another ring, you can measure its diameter by aligning it over a ruler from the zero mark to a reading on the ruler. Then, select the closest value available in the Inside diameter variable of our tool.

โœ… Use our tool in advanced mode by clicking the Advance mode button below our tool if your ruler can only measure in inches.

How to determine the ring size using the mm-to-ring size chart

After measuring your finger, you can also use the mm-to-ring size conversion chart below:

Inside Diameter (mm)

Inside Circumference (mm)

Sizes

UK & Australia

US & Canada

France

Germany

Japan

Switzerland

11.53

36.22

_

0

_

_

_

_

11.95

37.54

A

1/2

_

_

_

_

12.37

38.86

B

1

_

_

1

_

12.78

40.15

C

1 1/2

_

_

_

_

13.21

41.50

D

2

41 1/2

13 1/2

2

1 1/2

13.61

42.76

E

2 1/2

42 3/4

13 3/4

3

2 3/4

14.05

44.14

F

3

44

14

4

4

14.36

45.11

G

3 3/8

45 1/4

_

5

5 1/4

14.45

45.40

G 1/4

3 1/2<

_

14 1/2

_

_

14.56

45.74

G 1/2

3 5/8

_

_

6

_

14.65

46.02

H

3 3/4

46 1/2

_

_

6 1/2

14.86

46.68

H 1/2

4

_

15

7

_

15.04

47.25

I

4 1/4

47 3/4

_

_

7 3/4

15.27

47.97

I 1/2

4 1/2

_

15 1/4

8

_

15.40

48.38

J

4 5/8

49

15 1/2

_

9

15.70

49.32

J 1/2

5

_

15 3/4

9

_

15.80

49.64

K

5 1/8

50

_

_

10

16.00

50.27

K 1/2

5 3/8

_

10

_

16.10

50.58

L

5 1/2

51 3/4

16

_

11 3/4

16.51

51.87

M

6

52 3/4

16 1/2

12

12 3/4

16.92

53.16

N

6 1/2

54

17

13

14

17.35

54.51

O

7

55 1/4

17 1/4

14

15 1/4

17.75

55.76

P

7 1/2

56 1/2

17 3/4

15

16 1/2

18.19

57.15

Q

8

57 3/4

18

16

17 3/4

18.53

58.21

Q 3/4

8 1/2

_

18 1/2

17

_

18.61

58.47

R

8 5/8

59

_

_

19

18.89

59.34

R 3/4

9

_

19

18

_

19.10

60.00

S

9 1/8

60 1/4

_

_

20 1/4

19.41

60.98

S 3/4

9 1/2

_

19 1/2

19

_

19.51

61.29

T

9 5/8

61 1/2

_

_

21 1/2

19.84

62.33

T 1/2

10

_

20

20

_

20.02

62.89

U

10 1/4

62 3/4

_

21

22 3/4

20.20

63.46

U 1/2

10 1/2

_

20 1/4

22

_

20.32

63.84

V

10 5/8

63

_

_

23 3/4

20.68

64.97

V 1/2

11

_

20 3/4

23

_

20.76

65.22

W

11 1/8

65

_

_

25

21.08

66.22

W 3/4

11 1/2

_

21

24

_

21.18

66.54

X

11 5/8

66 1/4

_

_

26 1/4

21.49

67.51

Y

12

67 1/2

21 1/4

25

27 1/2

21.89

68.77

Z

12 1/2

68 3/4

21 3/4

26

28 3/4

22.33

70.15

Z+1

13

_

22

27

_

For example, you find out that you can wrap your finger with a 54.0 mm strip of paper end-to-end. From the chart above, the next inside circumference measurement of a ring size available is 54.51 mm. That means your finger ring size would be size 17 (US).

๐Ÿ™‹ Remember that, since our knuckles are not perfectly round, we choose the next one and not the closest smaller ring size.

If you found our mm-to-ring size converter useful, perhaps you may also enjoy reading our other related tools listed below:

Read more useful tips for determining your proper ring size in our ring size converter. ๐Ÿ˜Š

FAQ

How do I convert a millimeter measurement of my finger to a ring size?

To convert a measurement of your finger in millimeters to a ring size:

  1. Take a string and wrap it once around the finger you want to measure.
  2. Mark the string where it overlaps over itself.
  3. Using a ruler, measure the length of the string you marked.
  4. Check your ring supplier's chart for your ring size.
  5. You can also divide the string's length by ฯ€ or 3.14 if the supplier's chart asks for the equivalent diameter of your ring size.

What ring size measures 16 mm in diameter?

The 5 3/8 US and Canada ring size has an inside diameter of 16 millimeters. In UK and Australia, find the size K 1/2 if your ring measures 16 millimeters in diameter.

Kenneth Alambra
Measurements
Inside circumference
Select...
mm
Inside diameter
Select...
mm
Ring size equivalents
US & Canada
Select...
UK & Australia
Select...
France & Russia
Select...
Germany
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Switzerland
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Japan
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