What does EU/ISO ring size mean?

On this English page, EU/ISO size is treated as the inner circumference in millimeters, rounded to the nearest whole millimeter.

Can I measure ring size on a screen?

A screen chart is only a rough visual guide unless the display is calibrated. For expensive rings, use calipers, a jeweler's sizer or a printed guide checked at 100% scale.

Should wide rings be sized up?

Often yes. Wide bands create more contact with the finger and can feel tighter, so the calculator suggests checking a half size or full size up depending on width.

Ring Size Converter

Convert ring sizes by inner diameter, circumference, US size, UK/AU letters, EU/ISO circumference labels and JP sizes, with a band-width fit note.

Inner diameter (mm)

Inner circumference (mm)

US size (3-13)

EU/ISO size (circumference mm)

UK/AU size (letter)

Letters F-Z and half sizes are supported, for example M 1/2.

JP size (1-35)

Estimated size:

US 7

diameter 17.3 mm, circumference 54.3 mm

US/Canada scale

UK/AU

M 1/2

letter scale

EU/ISO

circumference mm

Japan scale

Band width (mm)

Fit recommendation

Standard band (3-5 mm): start with the measured size.

The screen ring scale is approximate. For an expensive purchase, use a jeweler's ring sizer, calipers, or a correctly printed size guide.

Bank card width on screen (px)

Calibration uses a standard card width of 85.60 mm. Without calibration, the scale is only a visual guide.

Full conversion table

Ring size conversion table
Diameter, mm	Circumference, mm	EU/ISO	US	UK/AU	JP
14.0	44.0	44	3	F	4
14.4	45.2	45	3.5	F 1/2	5
14.8	46.5	46	4	G 1/2	6
15.2	47.8	48	4.5	H 1/2	8
15.6	49.0	49	5	I 1/2	9
16.0	50.3	50	5.5	J 1/2	10
16.5	51.8	52	6	K 1/2	12
16.9	53.1	53	6.5	L 1/2	13
17.3	54.3	54	7	M 1/2	14
17.7	55.6	56	7.5	N	16
18.1	56.9	57	8	O	17
18.5	58.1	58	8.5	P	18
19.0	59.7	60	9	Q	20
19.4	60.9	61	9.5	R	21
19.8	62.2	62	10	S	22
20.2	63.5	63	10.5	T	23
20.6	64.7	65	11	U	25
21.0	66.0	66	11.5	V	26
21.4	67.2	67	12	W	27
21.8	68.5	68	12.5	X	28
22.2	69.7	70	13	Y	30
22.6	71.0	71	13.5	Z	31

Convert Ring Sizes by Diameter or Circumference

English ring-size searches usually compare US numbers, UK/AU letters, EU/ISO circumference labels and millimeter measurements. This converter keeps both inner diameter and inner circumference visible so the size can be checked against retailer charts.

EU/ISO is circumference, not diameter

EU/ISO ring labels commonly represent the inner circumference in millimeters. Older RU-style diameter labels are not used for the English page.

Measure Before You Buy

Measure the inside diameter of a well-fitting ring with calipers when possible.
For string or paper measurements, use inner circumference in millimeters and avoid stretching.
Wide rings often feel tighter than narrow rings, so check the wide-band note before ordering.
Printable or screen charts can be inaccurate unless the scale is verified.