Ring size·59 mm
Inside circumference
59 mm
US 9 · JP 19 · EU 59
Inside diameter 18.78 mm

59 mm inside — US 9, Japan 19

An inside circumference of 59 mm is an inside diameter of 18.78 mm. The US formula gives 8.8, so the size called in shops is 9; Japan and Korea say 19, and the EU (ISO 8653) size is 59.

At a glance

Divide the inside circumference by pi and you have the inside diameter; the US number comes from that diameter. The Japanese, Korean and EU sizes come straight from the circumference. Nothing here is copied from a chart — one measurement fixes the other three. It runs backwards too: knowing only US 6 gives a diameter, then 51.9 mm of circumference, and from there the other scales.

  • US and Canada9
  • Japan and Korea19
  • EU · ISO 865359
Inside circumference
59 mm
Inside diameter
18.78 mm
Diameter in inches
0.739 in
Nearest US half size
US 9 · 59.52 mm
Gap to that size
-0.52 mm
Where it sits
The common range

The US scale is defined in inches

US 0 has an inside diameter of 0.458 inch (11.63 mm) and each size adds 0.032 inch (0.8128 mm). So diameter = 11.63 + 0.8128 × size, and backwards, size = (diameter − 11.63) ÷ 0.8128. In circumference one size is 2.55 mm, which is where the saying “a size is a tenth of an inch” comes from — that is an approximation; the definition lives on the diameter. Shops only call half sizes, so this table prints the computed value next to the nearest half size.

Japan and Korea: circumference minus 40

Size = inside circumference in mm − 40. Size 13 is 53 mm, which lands near US 6.5; size 9 is 49 mm, near US 5. Korea uses the same numbering. Printed charts usually run from 1 (41 mm) to 27 (67 mm), so the two ends of this table are the same rule extended past what is printed — a shop may not stock those, and millimetres are the safer thing to say.

One step either way

0.5 mm smaller · 0.5 mm larger

58.5 mm
US 8.5JP 19
59.5 mm
US 9JP 20

Nearby sizes

59.5 mm
US 9JP 20
60 mm
US 9JP 20
60.5 mm
US 9.5JP 21
61 mm
US 9.5JP 21
61.5 mm
US 10JP 22
62 mm
US 10JP 22

The common range

46 mm
US 3.5JP 6
46.5 mm
US 4JP 7
47 mm
US 4JP 7
47.5 mm
US 4.5JP 8
48 mm
US 4.5JP 8
48.5 mm
US 4.5JP 9
49 mm
US 5JP 9
49.5 mm
US 5JP 10
50 mm
US 5.5JP 10
50.5 mm
US 5.5JP 11
51 mm
US 5.5JP 11
51.5 mm
US 6JP 12
52 mm
US 6JP 12
52.5 mm
US 6.5JP 13
53 mm
US 6.5JP 13
53.5 mm
US 6.5JP 14
54 mm
US 7JP 14
54.5 mm
US 7JP 15
55 mm
US 7JP 15
55.5 mm
US 7.5JP 16
56 mm
US 7.5JP 16
56.5 mm
US 8JP 17
57 mm
US 8JP 17
57.5 mm
US 8JP 18
58 mm
US 8.5JP 18
58.5 mm
US 8.5JP 19
59 mm
US 9JP 19
59.5 mm
US 9JP 20
60 mm
US 9JP 20
60.5 mm
US 9.5JP 21
61 mm
US 9.5JP 21
61.5 mm
US 10JP 22

Worth knowing

  • Inside circumference divided by pi is the inside diameter — every size here comes from that number.
  • US number = (inside diameter in mm − 11.63) ÷ 0.8128.
  • Japan and Korea: size = inside circumference in mm − 40. The EU (ISO 8653) uses the circumference itself.
  • The British letter scale is left out because no rule of the same reliability was confirmed — give the shop the millimetres.

Common questions

Q. What US size is 59 mm inside?

The formula gives 8.8, and the half size a shop would call is 9. US 9 measures 59.52 mm, so this cell sits -0.52 mm from it.

Q. What are the Japanese, Korean and EU sizes?

Size 19, and 59 in the EU (ISO 8653). The Japanese and Korean number is the circumference minus 40, so size 19 is 59 mm, while the EU size is the circumference itself.

Q. Which finger is this size for?

It sits in the band called “The common range”. 59 mm of circumference is 18.78 mm (0.739 in) across, and adult ring fingers mostly land between 46 and 62 mm. Above 78 mm you are in thumb and extended sizes.