InformationLifestyleUtilityEducation

Ring Size Chart

Convert ring sizes between US, UK, EU, Japan and Korea, find your size from a finger measurement in millimetres or inches, and check it against a true-to-scale circle on screen.

What did you measure?

mm= 52.0 mm around · 16.55 mm across

US / Canada

UK / AU

L½

EU / ISO

51.9

JP / KR / CN

Print-free size check

Calibrate the screen with any bank card, then lay a ring you own over the circle.

US 6 — inner diameter 16.52 mm

Place an existing ring on top. The inside edge of the ring should sit on the circle's outline.

US / CA	UK / AU / IE	EU / ISO	JP / KR / CN	Circumference	Diameter
3	F	44.2	4	44.2 mm	14.07 mm
3.5	G	45.5	5	45.5 mm	14.48 mm
4	H	46.8	7	46.8 mm	14.90 mm
4.5	I	48.0	8	48.0 mm	15.28 mm
5	J½	49.3	9	49.3 mm	15.69 mm
5.5	K½	50.6	10	50.6 mm	16.11 mm
6	L½	51.9	11	51.9 mm	16.52 mm
6.5	M½	53.1	12	53.1 mm	16.90 mm
7	N½	54.4	13	54.4 mm	17.32 mm
7.5	O½	55.7	14	55.7 mm	17.73 mm
8	P½	57.0	16	57.0 mm	18.14 mm
8.5	Q½	58.3	17	58.3 mm	18.56 mm
9	R½	59.5	18	59.5 mm	18.94 mm
9.5	S½	60.8	19	60.8 mm	19.35 mm
10	T½	62.1	20	62.1 mm	19.77 mm
10.5	U½	63.4	22	63.4 mm	20.18 mm
11	V½	64.6	23	64.6 mm	20.56 mm
11.5	W½	65.9	24	65.9 mm	20.98 mm
12	X½	67.2	25	67.2 mm	21.39 mm
12.5	Y	68.5	26	68.5 mm	21.80 mm
13	Z	69.7	27	69.7 mm	22.19 mm
13.5	Z+1	71.0	28	71.0 mm	22.60 mm
14	Z+2	72.3	29	72.3 mm	23.01 mm

If you have nothing to measure

Women — ring fingerUS 6 – 6.5 · 52 – 53 mm

Women — index / middleUS 5.5 – 6 · 51 – 52 mm

Men — ring fingerUS 9 – 10 · 60 – 62 mm

Men — index / middleUS 9.5 – 10.5 · 61 – 63 mm

Adjust for band width

up to 4 mmno change

5 – 6 mm+ ¼ US size

7 – 8 mm+ ½ US size

9 mm and up+ ½ to 1 US size

Every ring size is one number in disguise

A ring has exactly one physical dimension that matters: the inner circumference, in millimetres. ISO 8653 defines the international standard size as precisely that number, which is why a "European size 52" ring is 52 mm around the inside — no conversion needed.

Everything else is a national numbering scheme sitting on top of the same measurement. US sizes count in halves from an arbitrary zero, advancing about 0.8 mm of circumference per half size. British sizes use letters at roughly half that step, so the alphabet runs twice as fast. Japan, Korea and China share a numbered scale that steps about 0.6 mm at a time.

Once you know the circumference, every column in the chart follows. The diameter column is simply circumference divided by π — useful because measuring across a ring you already own is easier than threading something around a finger.

Measuring accurately

Half a millimetre is roughly half a US size, so technique matters more than the tool. The two reliable methods:

Around the finger

Cut a strip of paper about 5 mm wide — not string, which stretches. Wrap it snugly around the base of the finger, mark where it overlaps, and measure the marked length flat against a ruler. That length is the circumference.

Across an existing ring

Measure the inside edge to inside edge across the widest point, ideally with calipers. This is the more accurate of the two, and it is the method to use when buying a surprise gift.

Whichever you use, the ring has to clear the knuckle. If the knuckle is noticeably larger than the base of the finger, size to the knuckle and accept a slightly loose fit, or ask a jeweller about sizing beads.

Why the on-screen circle needs a bank card

Browsers have no idea how large your screen physically is — CSS pixels are not millimetres, and the ratio differs between a phone, a laptop, and a 4K monitor. Calibrating against an ID-1 card (85.60 × 53.98 mm, identical worldwide) converts pixels to millimetres for your display, which is what makes a true-size circle possible without printing anything.

Fingers change size during the day

Temperature is the big one. Cold fingers can be a full size smaller than warm ones. Measure at room temperature, never straight after being outside in winter.
Time of day. Fingers are smallest in the morning and largest in the late afternoon and evening. Measure at the end of the day so the ring is not tight at its worst moment.
Salt, alcohol and heat all cause fluid retention that can add half a size temporarily.
Pregnancy and weight change shift ring size substantially — often more than a full size.
Dominant hand. The same finger on your dominant hand is usually about a quarter to half a size larger.
Measure three times on different days and take the middle value. A single reading is the most common reason a ring arrives wrong.

Band width, fit style, and resizing

A wide band contacts more of the finger and reads as tighter at the same nominal size. Jewellers routinely add a quarter to a half size for bands over 6 mm, and up to a full size beyond 9 mm.

Comfort-fit bands are domed on the inside so only the centre touches the skin. They slide over the knuckle more easily and generally run a quarter to a half size large — order down accordingly. Standard flat-interior bands do not need the adjustment.

Most plain metal rings can be resized up or down by one to two sizes. What usually cannot: full eternity bands with stones all the way round, tungsten carbide and ceramic (too hard to work), titanium (difficult and rarely offered), and anything with an intricate pattern that would be broken by cutting. For those, getting the size right the first time is the only option.

Buying a surprise ring

Borrow a ring they already wear on the correct finger — this is by far the most accurate route. Measure the inner diameter, or press it into soap to keep an impression.
Trace the inside on paper if you cannot take the ring away, then measure the traced circle. Less precise but usable.
Fall back on averages. US 6 to 6.5 for women and US 9 to 10 for men are the most commonly sold sizes, and are a reasonable guess if all else fails.
Err slightly large. A loose ring can be worn temporarily with a sizer insert; a ring that will not go past the knuckle cannot be worn at all.
Check the resizing policy before ordering, especially for eternity bands and hard metals where resizing is impossible.