Ring Size Converter

Convert finger circumference or ring diameter to US, UK, EU, Japanese and Swiss ring sizes instantly — free, accurate, and with no sign-up.

How to Use This Ring Size Converter

1. Measure your finger or ring. Wrap a strip of paper or string around your finger and measure its length in millimetres, or measure the inside diameter of a ring that already fits.
2. Choose your starting point. Use the “By Measurement” tab for circumference or diameter, or the “By Ring Size” tab if you already know a size in one country’s system — a US ring size, a UK letter, an EU number, or a Japanese size.
3. Type your value. The converter updates instantly and shows your ring size conversion in every major system at once.
4. Read the diameter and circumference too. The tool shows the exact inside diameter and inside circumference in millimetres and inches, so you can order from any jeweller in any country with confidence.
5. Tap any row of the ring conversion chart below to load that standard size into the converter and compare its equivalents.

How to Measure Ring Size at Home

You do not need a jeweller’s mandrel or a plastic ring sizer to find your size. You need a strip of paper, a piece of string, or dental floss, plus a ruler with millimetre markings. Wrap the strip around the base of the finger that will wear the ring, pull it snug without squeezing, and mark the point where the end overlaps. Lay it flat, measure the marked length in millimetres, and you hold your finger circumference — the single most useful ring measurement. Type it into the ring size calculator circumference field above and the converter does the rest.

Measure the exact finger on the exact hand. Your dominant hand usually runs about half a size larger, and fingers swell during the day, in warm weather, and after exercise. Measure at the end of the day, at room temperature, and repeat the measurement two or three times. If your knuckle is much wider than the base of your finger, measure both places and pick a size between the two readings, so the ring slides over the knuckle yet stays put at the base.

How to Determine Your Ring Size With a Ring You Already Own

The inside diameter method is the most accurate home method, and it is the method OnlineConversion-style charts rely on too. Take a ring that fits the correct finger perfectly, lay it on a flat surface, and measure straight across the inside of the band from one inner edge to the opposite inner edge. Measure the inside, never the outside, because band thickness changes from design to design while the inside diameter decides the fit. Enter that number into the diameter ring size mode above. A 16.5 mm inside diameter equals a US size 6; a 17.3 mm diameter equals a US size 7; a 19.8 mm diameter equals a US size 10.

The string and paper method, step by step

1. Wrap a piece of string or a strip of paper around your finger at the base.
2. Mark the point where the two ends meet.
3. Measure the string or paper against a ruler to get the circumference of your finger.
4. Divide that number by 3.14 to get the diameter of your finger — or skip the maths and use this converter.
5. Look up your ring size in the ring conversion chart below.

Other reliable ways to check your finger size

A local jeweller measures you free in under a minute with a mandrel and a set of sizing rings, and gives you the most precise answer. Printable ring size charts work well too, if you print them at exactly 100% scale and check the test ruler on the sheet first. Plastic belt-style ring sizers cost very little, stay reusable for years, and suit anyone who buys rings often.

Ring Conversion Chart

Use this international ring conversion chart to compare US & Canada numbers, UK & Australia letters, EU (ISO) sizes, and Japanese sizes side by side with the inside diameter and inside circumference in millimetres and inches. Tap any row to load that size into the converter.

Circumference to Ring Size: How the Conversion Works

Circumference to ring size conversion starts with one simple fact: every ring size in every country describes the same circle. The inside circumference — the length around the inside of the band — anchors every system. Jewellers measure ring sizes in cm circumference terms on much of the planet, because the EU and ISO 8653 standard simply prints the circumference in millimetres as the size itself. An EU 52 ring measures exactly 52 mm around the inside.

To move from circumference to diameter ring size values, divide the circumference by π (3.14159). A 54.4 mm circumference ÷ π gives a 17.3 mm inside diameter, and the US mandrel scale turns that diameter into a US size 7. To go the other way, multiply the diameter by π. This rings size converter performs both steps instantly and then translates the result into the letter scale of the UK and Australia, the number scale of Japan, and the Swiss scale, which subtracts 40 from the circumference. Worked examples: 44.2 mm of circumference gives US 3 (UK F), 49.3 mm gives US 5 (UK J), 56.9 mm gives US 8 (UK P), and 62.1 mm gives US 10 (UK T).

US Ring Size Converter: International Ring Size Systems Explained

The United States and Canada number their rings from about 0 to 16, rising by roughly 0.8 mm of diameter per full size. The UK, Ireland, Australia, and New Zealand use letters from A to Z, with half letters between them; a finger size conversion from letters to numbers confuses many shoppers, which is exactly why a us ring size converter earns its keep. France and Switzerland historically subtract 40 from the circumference, Germany often prints the inside diameter itself, and Japan numbers its rings on its own scale where a US 7 becomes a Japanese 14.

Brands add one more complication: each jeweller cuts to a chart that may differ by a fraction of a millimetre from the standard. Treat this converter’s output as the correct standard size, then check the specific retailer’s chart before you pay — especially for an engagement ring, a wedding band, or an eternity ring you plan to wear daily for decades. When a measurement lands between two standard sizes, this tool flags it and recommends the larger size.

Ring Size Guide: Useful Tips for a Perfect Fit

• Measure the right finger on the right hand. The same finger differs between hands, and the dominant hand usually needs the larger size.
• Measure at the end of the day. Fingers shrink in the cold and swell with heat, salt, and exercise, so evening measurements at room temperature give the safest reading.
• Go up a size for wide bands. Rings wider than 6 mm — most comfort-fit wedding bands — feel tighter, so add a quarter to a half size.
• Check the size a few times. A ring should slide on with slight resistance over the knuckle, sit snugly at the base, and never squeeze hard enough to leave deep marks.
• Remember that resizing has limits. Plain bands usually resize one to two sizes; pavé, eternity, and engraved designs may not resize at all, so accuracy matters most exactly there.

Why Use This Ring Size Converter

• Every system in one place. US & Canada, UK & Australia, EU (ISO), Japan, Switzerland, France, and Germany — plus diameter and circumference in millimetres and inches.
• Three ways in. Start from finger circumference, from inside diameter, or from a ring size you already know; the converter handles circumference to ring size and diameter ring size lookups equally well.
• Instant and free. No sign-up, no modal, no waiting — the result updates as you type and works on any phone.
• Between-size warning. The tool tells you when your measurement falls between two standard sizes instead of silently rounding the wrong way.
• A chart that works. Every row of the ring conversion chart loads into the tool with one tap, so checking a size takes seconds.

Who Is This Ring Size Converter For?

Engagement ring buyers who must find a partner’s size in secret and convert it before ordering online. Online jewellery shoppers who face a foreign size chart — a UK letter, an EU number, a Japanese size — at checkout and need a finger size conversion they can trust. Couples ordering wedding bands abroad, where the same finger wears a different label in every country. Jewellery sellers and Etsy shop owners who answer “what size is 52 mm?” questions daily and need a fast, standard answer. Gift buyers shopping for promise rings, anniversary bands, and fashion rings who only have an old ring to measure.

Average Ring Sizes for Women and Men

The average US ring size for women is 6 to 7 (a circumference of about 51.8 to 54.4 mm, UK L to N). The average for men is 9 to 10 (about 59.5 to 62.1 mm, UK R to T). The most commonly stocked sample size in jewellery stores is a women’s size 7 and a men’s size 10. Averages only guide a guess — heights, hand shape, and knuckle width move individual sizes well outside these ranges — but they give surprise buyers a sensible starting point and a reminder to size slightly up, because a jeweller removes metal more easily than they add it.

How to Find a Partner’s Ring Size in Secret

Surprise proposals create the hardest sizing problem of all. The most reliable trick borrows a ring your partner already wears on the correct finger: measure its inside diameter with a ruler or caliper, trace its inner circle onto paper, or press it into a bar of soap and measure the impression later. A second trick slides their ring onto your own finger and marks where it stops. Friends and family often know the size or can stage a casual jewellery-store visit. If every route fails, start from the averages above, choose the slightly larger size, buy from a seller with free resizing, and keep the proposal stress-free.

Frequently Asked Questions

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