Question 1

How accurate is an online ring sizer?

Accepted Answer

After calibrating with a real card, on-screen measurement is typically within half a size. For expensive purchases, confirm with a jeweler.

Question 2

Why do I need to calibrate my screen?

Accepted Answer

Every screen has a different pixel density. Matching a standard 85.6mm card lets us convert pixels into true millimeters.

Question 3

What time of day should I measure?

Accepted Answer

Measure at the end of the day when fingers are warm and slightly larger. Avoid measuring when cold.

Question 4

What if I'm between two sizes?

Accepted Answer

Choose the larger size, especially for wide bands (6mm+), which fit more snugly.

Question 5

Is my dominant hand bigger?

Accepted Answer

Usually yes — by up to half a size. Measure the exact finger on the hand you'll wear it on.

Question 6

How do US, UK, EU and JP sizes compare?

Accepted Answer

US and JP use numbers, UK uses letters, and EU sizes equal the inside circumference in millimeters. See the chart above.

US	UK	EU	JP	Ø mm	Circ. mm
3	F	44	4	14.1	44.2
3.5	G	45	5	14.5	45.5
4	H	47	7	14.9	46.8
4.5	I	48	8	15.3	48.0
5	J½	49	9	15.7	49.3
5.5	K½	51	10	16.1	50.6
6	L½	52	12	16.5	51.9
6.5	M½	53	13	16.9	53.1
7	N½	54	14	17.3	54.4
7.5	O½	56	15	17.7	55.7
8	P½	57	16	18.1	57.0
8.5	Q½	58	17	18.5	58.2
9	R½	60	18	18.9	59.5
9.5	S½	61	19	19.4	60.8
10	T½	62	20	19.8	62.1
10.5	U½	63	22	20.2	63.3
11	V½	65	23	20.6	64.6
11.5	W½	66	24	21.0	65.9
12	Y	67	25	21.4	67.2
12.5	Z	68	26	21.8	68.5
13	Z+1	70	27	22.2	69.7

Online
ring sizer.

First, your screen.