Ring Size Converter

What's my ring size in another country? Enter your size in US, UK, EU, or Japan/Korea format — or the millimeters you measured — and see every match instantly.

I know my size in Your ring size

Pick a size above to see the conversion

Ring width and metal thickness can shift a comfortable fit by half a size — treat this chart as a close estimate, not a guaranteed fit.

Every conversion runs in your browser — nothing you enter is sent to a server.

Reading a ring size chart without the guesswork

Ring sizing is one of the most confusing things to shop for online: the US/Canada, UK/Australia, EU, and Japan/Korea systems each count differently, and none of them convert to another with simple mental math. This converter skips the guesswork by looking your size up directly in a published ring size chart — the same numbers stamped inside real rings — rather than calculating an approximate formula.

How the ring sizing systems differ

US / Canada uses a numeric scale from roughly 3 to 16, with half sizes in between (a full size step is about 0.4 mm of diameter).
UK / Australia / Ireland uses letters A through Z, with a half-letter (½) step between most adjacent US half sizes.
EU (ISO 8653) is defined as the finger's circumference in millimeters — so an EU size of 54 literally means a 54 mm circumference, no lookup required for that step alone.
Japan / Korea (号) uses its own ascending number scale, roughly one unit per 1.3 mm of circumference; critically, Japan and Korea share the exact same numbers, so a Japanese 号14 and a Korean 14호 are the same ring.
Inside diameter (mm) is the straight-line width of the opening rather than the distance around it — useful when you're measuring an existing ring rather than your finger.

Worked example. A US size 7 ring is UK N½, has an EU circumference of 54.4 mm, is a Japan/Korea 号14, and has a 17.3 mm inside diameter — all four numbers describe the exact same physical ring opening, just counted differently.

Full ring size conversion chart

These are the complete lookup values this converter uses — the same numbers feed the interactive tool above, so switching the "I know my size in" system there always matches a row below.

US / CA	UK / AU	EU (mm)	Japan / Korea (号)	Diameter (mm)
3	F	44.0	4	14.1
3.5	G	45.5	5	14.5
4	H	46.8	7	14.9
4.5	I	48.0	8	15.3
5	J½	49.3	9	15.7
5.5	K½	50.6	10	16.1
6	L½	51.9	12	16.5
6.5	M½	53.1	13	16.9
7	N½	54.4	14	17.3
7.5	O½	55.7	15	17.7
8	P½	57.0	17	18.1
8.5	Q½	58.3	18	18.5
9	R½	59.5	19	18.9
9.5	S½	60.8	21	19.3
10	T½	62.1	22	19.7
10.5	U½	63.4	23	20.1
11	V½	64.6	24	20.5
11.5	W½	65.9	26	20.9
12	X½	67.2	27	21.3
12.5	Y½	68.5	28	21.7
13	Z½	69.7	29	22.2

This chart covers the half-size range most adult rings are sold in (roughly a small women's size up to a large men's size). If your measurement falls slightly outside it, the converter above shows the closest matching row instead of refusing to answer.

How to measure your ring size at home

Method 1: string or paper strip (measures circumference)

Cut a thin strip of paper, or use a piece of string or ribbon that won't stretch.
Wrap it snugly around the base of the finger you'll wear the ring on — snug enough to stay on, loose enough to slide over the knuckle.
Mark the exact point where the strip overlaps itself with a pen.
Lay the strip flat and measure the marked length against a ruler, in millimeters.
Enter that number into the EU (circumference, mm) field above to see the matching US, UK, and Japan/Korea sizes.

Method 2: an existing ring that already fits (measures inside diameter)

Find a ring that already fits the intended finger comfortably — not a ring worn on a different finger, and not a very wide statement ring, which fits tighter than a thin band of the same size.
Place the ring flat on a ruler, or on a printable ring-sizing chart.
Measure straight across the inside opening, at its widest point, in millimeters.
Enter that number into the Inside diameter (mm) field above to see the matching US, UK, EU, and Japan/Korea sizes.

Tips for getting an accurate size

Time of day matters: fingers swell slightly through the day and in warm weather, and shrink in the cold. Measure in the evening for the most reliable everyday size, and avoid measuring right after exercise or in cold weather.
Measure the exact finger: ring size can differ noticeably between fingers on the same hand, and even between your left and right hand.
Wider bands need extra room: a band wider than about 6 mm typically needs to be a half size larger than a thin band to feel the same, since more metal touches the finger.
Between two sizes? Sizing up is usually safer than sizing down — a slightly loose ring can be resized smaller more easily (and more cheaply) than a too-tight ring can be stretched.

Why a general chart isn't a substitute for professional sizing

Unlike shoe or clothing sizes, ring sizing directly touches skin with no ease built in, so small measurement errors matter more. This converter's chart matches the standard lookup tables used across the jewelry trade, but knuckle size, finger shape, and the exact width and metal of a specific ring can all shift what feels comfortable by half a size. For an important purchase — especially an engagement ring — a jeweler's metal ring sizer, tried on in person, is always more reliable than a string or a printed chart.

Sources & further reading

Frequently asked questions

How do I convert a US ring size to UK, EU, or Japan/Korea size?

Choose the system you already know at the top of the converter — US/CA, UK/AU, EU circumference, Japan/Korea 号, or a measured diameter in mm — and pick or enter your size. The other systems are read straight off a size chart, not calculated from a formula, so the numbers match what's stamped inside real rings. For example, a US size 7 converts to UK N½, EU 54.4 mm circumference, Japan/Korea 号14, and a 17.3 mm inside diameter.

How do I measure my ring size at home with string or paper?

Wrap a strip of paper, ribbon, or non-stretchy string snugly around the base of your finger, mark the point where it overlaps, then lay it flat against a ruler and measure the length in millimeters — that number is your finger's circumference. Enter it into the EU (circumference, mm) field of this converter to see the matching US, UK, and Japan/Korea sizes. Measure at the end of the day when fingers are largest, and avoid measuring when your hands are cold, since fingers shrink slightly in the cold.

How do I find my size from a ring I already own?

Lay the ring flat on a ruler or printable ring sizer and measure the inside opening — the widest straight-line distance across the hole — in millimeters; that's the inside diameter. Enter that number into the Inside diameter (mm) field to see the matching US, UK, EU, and Japan/Korea sizes. This method only works with a ring that already fits the intended finger, since the outside diameter or a ring worn on a different finger will give the wrong size.

Are Japanese and Korean ring sizes the same?

Yes — Japan and Korea both use the same 号 (ho/ho-su) numbering system, so a Japanese size 14 ring is identical to a Korean 14호 ring; this converter's Japan/Korea column covers both. The scale isn't linear with US or EU sizes, which is why looking the number up on a chart, rather than doing quick mental math, avoids ordering the wrong size online.

Does this converter handle half sizes, and is my size sent anywhere?

Yes — the US/CA and UK/AU dropdowns include every half size from 3 to 16 (and F to Z+6), which covers the range most adult rings are sold in. And no, nothing is sent anywhere: this ring size converter runs entirely in your browser, so the size you enter or measure never leaves your device and isn't stored on any server.