Ring Sizes (Size Numbers) and Inner Diameter

Ring sizes are shown using the size numbers commonly used in Japan.

The approximate inner diameter (the diameter of the inside of the ring) for each size number is as follows.

Ring Size Chart

Size	Inner diameter (mm)	Inner circumference (mm)
No. 1	13.0	40.8
No. 2	13.4	41.9
No. 3	13.7	42.9
No. 4	14.0	44.0
No. 5	14.4	45.0
No. 6	14.7	46.1
No. 7	15.0	47.1
No. 8	15.4	48.2
No. 9	15.7	49.2
No. 10	16.0	50.3
No. 11	16.4	51.3
No. 12	16.7	52.4
No. 13	17.0	53.4
No. 14	17.4	54.5
No. 15	17.7	55.5
No. 16	18.0	56.5
No. 17	18.4	57.6
No. 18	18.7	58.6
No. 19	19.0	59.7
No. 20	19.4	60.7
No. 21	19.7	61.8
No. 22	20.0	62.8
No. 23	20.4	63.9
No. 24	20.7	64.9
No. 25	21.0	66.0
No. 26	21.4	67.0
No. 27	21.7	68.0
No. 28	22.0	69.1
No. 29	22.4	70.1
No. 30	22.7	71.2

How to Choose a Ring Size and Important Notes

The inner diameter is a useful guide when judging size, but it can be difficult to determine the exact size or how a ring will feel from the inner diameter alone.

Even at the same size, a ring can feel different depending on its width, thickness, inner shape and design.

Finger size can also change with the time of day, temperature, physical condition and swelling.

For this reason, when choosing a ring size, we recommend that you do not rely on the inner diameter figure alone, but check your actual finger size using a ring gauge.

Please note that the chart above is a general guide to ring sizes in Japan, and there may be slight variations between products.

Frequently Asked Questions

Q. What size is a ring with an inner diameter of 16mm?

A. In Japanese ring sizes, it is roughly equivalent to No. 10.

Q. Can I decide on a size from the inner diameter alone?

A. The inner diameter is a useful reference, but because a ring's width and shape affect how it feels, we do not recommend deciding from the inner diameter alone.

Q. Why do rings of the same size differ in tightness?

A. Because the area in contact with the finger differs depending on the ring's width, thickness and inner shape. Wide rings in particular may feel tighter than narrow rings.

Q. How can I check which ring size is right for me?

A. We recommend using a ring gauge and trying it on your finger to check the size.