Ring size chart: US, UK, EU, Japan and millimetres

How each system defines a size

Ring size charts look like they disagree because they do: each system was built on a different ruler. Before converting, it helps to know what the numbers mean.

• US and Canada. A numerical scale in quarter steps. Each whole size adds 0.8128 mm of inside diameter (0.032 in), which Wikipedia also expresses as 2.55 mm of circumference. Size 7 is about 17.3 mm across.
• UK, Ireland, Australia, New Zealand. Letters A to Z with half sizes (M½, N½), and Z+1, Z+2 above Z. Each letter step is 0.4064 mm of diameter, so two letters are roughly one US size.
• EU / ISO 8653. The inside circumference in millimetres, used across continental Europe. An EU 54 is a ring with a 54 mm circumference, which is a 17.2 mm diameter. Because it is a physical measurement rather than a code, it is the least ambiguous of all the systems.
• Japan. Whole numbers starting at 1 for a 13 mm diameter, with each step adding a third of a millimetre. A Japanese 15 is about 17.7 mm across. The same scale is used widely in China, Korea, Hong Kong and Taiwan.
• Russia and much of the former USSR. The inside diameter in millimetres, in half steps: 16, 16.5, 17 and so on. If you see a "17" on a Russian site, it means 17 mm.

The two measurements are tied together by one formula: circumference = diameter × 3.1416. Every row in the chart below starts from the diameter and works outward.

Ring size conversion chart

The table runs from 14 to 23 mm of inside diameter in half-millimetre steps, which is the range covered by Orbita. US sizes are rounded to the nearest quarter, UK to the nearest half letter and Japanese sizes to the nearest whole number. For the EU column the circumference is the size.

Inside diameter, mm	Circumference, mm (EU / ISO 8653)	US / Canada	UK / AU	Japan
14.0	44.0	3	F	4
14.5	45.6	3½	G	5
15.0	47.1	4¼	H½	7
15.5	48.7	4¾	I½	8
16.0	50.3	5½	J½	10
16.5	51.8	6	L	11
17.0	53.4	6½	M	13
17.5	55.0	7¼	N½	14
18.0	56.5	7¾	O½	16
18.5	58.1	8½	Q	17
19.0	59.7	9	R	19
19.5	61.3	9¾	S½	20
20.0	62.8	10¼	T½	22
20.5	64.4	11	V	23
21.0	66.0	11½	W	25
21.5	67.5	12¼	X½	26
22.0	69.1	12¾	Y½	28
22.5	70.7	13¼	Z½	29
23.0	72.3	14	Z+2	31

The chart is the same for men and women. Men's rings typically fall between US 9 and 12 (19 to 21.5 mm) and women's between US 5 and 8 (15.7 to 18 mm), but the only number that matters is the one for the finger in question.

Why your chart and the shop's chart disagree

Compare three jewellers' charts and you will find rows that differ by a quarter size, sometimes a half. None of them is necessarily wrong.

• The steps do not line up. A US step is 0.81 mm, a UK letter is 0.41 mm, a Japanese step is 0.33 mm. Rounding the same diameter into each scale lands in different places depending on where the chart's author started.
• Half sizes get dropped. Simplified UK charts skip the half letters, so US 7 appears as N on one chart and N½ on another. Brilliant Earth, for instance, lists US 7 as N½ and EU 54.5.
• Some charts round the EU column to whole numbers. A 54.4 mm circumference becomes "54" on one chart and "55" on another.
• Manufacturers' mandrels differ slightly. The physical sizing tools used by jewellers are not all calibrated identically, and a ring sold as a size 7 in one country can measure a fraction differently from a size 7 made elsewhere.

The practical rule: when ordering from abroad, use the retailer's own chart if it has one, and compare millimetres, not size labels. A diameter or circumference in mm is unambiguous; "size 7" is not. If a product page gives only a label, ask the seller for the inside diameter of that specific ring.

US to UK, EU and Japan: the sizes people search for most

• US 5 is about 15.7 mm: UK J (some charts say J½), EU 49 to 49.5, Japan 9.
• US 6 is 16.5 mm: UK L to L½, EU 52, Japan 11 to 12.
• US 7 is 17.3 mm: UK N to N½, EU 54 to 54.5, Japan 14 to 15.
• US 8 is 18.1 mm: UK P to P½, EU 57, Japan 16.
• US 9 is 18.9 mm: UK R to R½, EU 59.5, Japan 19.
• US 10 is 19.8 mm: UK T to T½, EU 62, Japan 21.
• US 11 is 20.6 mm: UK V to V½, EU 64.5, Japan 24.

Notice that every whole US size lands on a whole UK letter two steps apart (J, L, N, P and so on); the half letters appear on charts that round from circumference rather than diameter. Where a range is shown, the right choice depends on band width: wider bands go to the larger size.

How to find your size from a finger measurement

1. Wrap a strip of paper around the base of the finger and mark the overlap.
2. Measure the length in millimetres. That is your circumference and your EU size.
3. Find the nearest circumference in the chart and read the US, UK or Japanese size in the same row.

For example, a 56.5 mm circumference is EU 56.5, an 18 mm diameter, US 7¾, UK O½ and Japan 16. The full method, with its pitfalls, is in our guide to how to measure ring size at home.

How to find your size from a ring that fits

Measure the inside diameter across the widest point, in two directions, and average. Find that diameter in the first column. If you are reading with a ruler marked in whole millimetres, you will land between rows most of the time; calipers or an on-screen sizer that moves in 0.1 mm steps remove that guesswork.

Notes on UK and Japanese sizes

Because a UK letter is only 0.41 mm, a chart in half-millimetre steps has to skip letters. That is why K, P and U are missing from the table above: they fall between rows. If a British retailer lists a half size, such as N½, look for the nearest millimetre value in their own chart rather than rounding to a whole letter.

Japanese sizes are finer still, a third of a millimetre each, so one row of our chart spans one and a half Japanese sizes and the column advances by one or two per row. Japanese retailers usually show the circumference in millimetres next to the size number; when they do, that is the number to use.

Band width and comfort fit

The chart describes the hole in the ring, not how it feels. A 2 mm band and an 8 mm band of the same size sit differently: the wide one covers more skin and is harder to push over the knuckle, which is why jewellers suggest sizing up half a size for bands over about 4 mm. A comfort-fit profile, rounded on the inside, slides on more easily than a flat one and may fit true to size or a touch large.

Using the chart when buying online

1. Get your inside diameter or circumference in millimetres.
2. Work out which system the listing uses: a number between 40 and 75 is almost always EU, 3 to 14 is US, a letter is UK, and a number between 1 and 30 with a Japanese or Chinese seller is JP.
3. Convert with the retailer's chart or the one above.
4. If you land between rows, consider band width, and check whether the ring can be resized before you commit.

A chart that converts for you

If you have a ring that fits, you do not need to read the table at all. In Orbita you place the ring on the screen of an iPhone or iPad, drag the circle until it matches the inside edge, and the app shows the diameter, the circumference and the size in US, UK, EU, JP or RU, interpolating between the rows above. The scale is set from the physical diagonal of your device model, so the circle on screen really is the size it claims. The app is free and works without an internet connection.