Ring size chart: US, UK, EU, mm and Japanese sizes in one table

A ring size chart converts one country's ring size into another's. The safest number to compare is the inner diameter or inner circumference of the ring in millimetres, because every system is built on one of those two measurements. A US 7 is 17.3 mm across the inside and 54.4 mm around it, which is an EU 54, a UK N½ and an Italian 14.

Below you will find the full table from US 3 to US 13, how to measure your ring size at home, and where published charts disagree. The last part is for jewelry store owners selling on Shopify.

International ring size chart (US, UK, EU, mm)

Read across a row. The two millimetre columns define the sizes; the rest are each country's label for them.

US to UK ring size, EU to US and the other rules

• US and Canada sizes go up in quarter steps, and each whole size adds about 0.81 mm to the inner diameter (diameter = 0.8128 × US size + 11.63 mm).
• UK, Ireland and Australia use letters with half sizes. Since a 1987 British Standard, one letter equals 1.25 mm of circumference, and size C is 40 mm around.
• EU sizes follow ISO 8653, which defines ring sizes by the inner circumference in millimetres. EU 54 is a ring about 54 mm around the inside. Germany and the Netherlands often use the inner diameter in mm instead, so a German "17" usually means 17 mm across, close to a US 6½ or 7.
• Italy, Spain and Switzerland use the circumference minus 40. Italian 14 is a 54 mm circumference, the same ring as EU 54.
• Japan uses the JCS number scale, where size 1 is 13.0 mm across and each size adds a third of a millimetre. Japanese 13 is 17.0 mm across and 53.4 mm around.

Where ring size charts disagree

If you compare this table with a jeweller's chart, some rows will not match exactly. These are the differences we found, and they are normal:

• Japanese sizes. Blue Nile and Wikipedia list one Japanese size lower than our table at US 6 and from US 8½ upward (for example US 10 as Japanese 20, where we give 21), and two lower at US 13 (27, where we give 29). Our column is calculated from the Japanese JCS rule, which the Japanese converter we used also follows. When in doubt, ask for the inner diameter in mm.
• UK letters at the edges. Wikipedia gives US 8½ as Q¼ and US 12½ as Y½. Blue Nile gives Q½ and Z, and puts small sizes such as US 3½ half a letter higher.
• Swiss sizes. Blue Nile's Swiss column uses quarter sizes and does not follow the "circumference minus 40" rule exactly. In the middle of the range it runs up to about one size higher (US 7 is 15¼ there, 14 here).
• Brand sizing. Pandora labels its rings with its own European-style numbers, and charts of its rings map Pandora 50 to US 5, where our table has EU 49. If you sell a brand that sizes this way, use the brand's own chart.
• China and Hong Kong. Both use a number scale that looks like the Japanese one, but Blue Nile's Hong Kong column sits one or two numbers higher (US 7 is 15). Published Chinese tables do not agree with each other, so we left China out of the main table rather than guess.

Labels can drift by half a size between sources, but the millimetres stay the same.

How to measure your ring size at home

You need a ruler with millimetres and about two minutes. There are two reliable methods.

Method 1: string or paper strip

1. Cut a thin strip of paper, or use a piece of string or dental floss that does not stretch.
2. Wrap it around the base of the finger that will wear the ring. It should be snug but not tight.
3. Mark the point where the end overlaps.
4. Lay it flat and measure from the end to the mark in millimetres.
5. That length is your circumference. Find the closest value in the circumference column, or read it as an EU size directly (54 mm is EU 54).

Method 2: a ring that already fits

1. Pick a ring that fits the same finger well. A thin, round band works best.
2. Measure straight across the inside, from inner edge to inner edge, at the widest point.
3. That is your inner diameter. Match it to the diameter column.

Nothing stretches or bends, so this is the more accurate method, and the one to use when buying a ring as a surprise.

Tips that change the result

• Measure at the end of the day. Fingers are smaller in the morning and in the cold, and larger after exercise or in heat. Blue Nile's guide says to measure in the evening, so the ring stays comfortable after a normal day.
• Check the knuckle. If your knuckle is much wider than the base of your finger, measure both and choose a size between them. The ring has to slide over the knuckle and still not spin at the base.
• Wide bands need about half a size more. A wide band covers more skin and feels tighter than a thin one of the same size.
• Between two sizes, take the larger one. A slightly loose ring can be fixed with a sizing insert. A tight one cannot be worn.
• Measure two or three times. A 1 mm error in circumference is almost half a US size.

Why we do not offer a printable ring sizer

Printable sizers only work if the page prints at exactly 100%. Many PDF viewers and printers default to "fit to page", and a sizer printed at 97% shrinks every circle by more than half a US size. Even Blue Nile's printable chart asks you to check the scale with a credit card first. A ruler and a ring you own avoid that risk.

For jewelry store owners: ring sizes on Shopify

Most ring sizing complaints come from three gaps. Either the shopper does not know their size, knows it in another system, or the ring fits differently than expected. The fixes cost less than one returned ring that has to be inspected, cleaned and resized. We build Shopify apps, including a size chart app, and this is what we would set up first.

Name ring size variants with the system

Shopify allows up to three options and up to 2,048 variants per product, so a full run of half sizes fits easily. Name the option Ring size and put the system in the value:

Keep the values consistent across products, because filters and AI shopping agents read variant names as data.

Show sizes per country on the product page

Put the ring size chart link next to the size picker, with inner diameter and circumference in mm and the home measuring steps.

If you sell to several countries, show each shopper their own system first. Shopify themes can read the shopper's country from the Liquid localization object, as we explain in our clothing size conversion chart guide. A shopper in London should not have to scan for the UK column in a seven-column table on a phone.

Plainfee Size ChartsSize charts that show every shopper their own country's sizes, with how-to-measure steps in 31 languages.See how it works

Plainfee Size Charts has a ready-made rings chart with US, UK, EU, Italian and Japanese sizes and inner diameter, and it shows each shopper their own country's sizes first, in 44 countries. The free plan covers 3 live charts, and Pro is a flat $14.99 a month with no fees per order. If you want to compare it with other options first, our list of Shopify size chart apps covers Kiwi, which has a fit recommender we do not offer, and four others. Setup is in the guide to adding a size guide to your theme.

Reduce ring-size returns

• Sell or send a ring sizer. A plastic multi-sizer costs little and removes the guesswork. Blue Nile, for one, sends a free plastic sizer.
• Offer half sizes. A shopper "between sizes" is usually a half size. If you stock only whole sizes, say whether you can resize to halves.
• Offer free resizing instead of a refund. The same retailer includes free resizing for the first year, within what each ring allows. For plain bands this is often cheaper than processing a return.
• Say which rings cannot be resized. If a style cannot be resized, or only within a small range, state it on that product page before checkout.
• Set return rules per product. Shopify's return rules let you mark products or collections as final sale and set different return windows for specific products or variants. Use this for engraved or custom-sized rings, and say so before checkout. If you charge for returns, our comparison of Shopify return fees shows the options.
• Answer size questions in the chart. When someone emails "is EU 54 a US 7?", add the answer to the chart.

For ideas on how established jewellers lay this out, see our roundup of Shopify jewelry store examples.

A quick checklist before you publish a ring

• Variant values name the system (US 7, not 7).
• The size chart link sits next to the size picker.
• The chart includes inner diameter and circumference in mm.
• Measuring steps cover string, existing ring, end of day and wide bands.
• Resizing, half sizes and non-resizable styles are stated on the page.
• Final sale rings are set in Shopify return rules and named before checkout.
• You checked the chart on a phone.

Every country labels the same few millimetres differently. Give shoppers the millimetres, their own label and an easy way to measure, and most sizing questions end before they become returns.

Frequently asked questions