Ring Size Calculator
By Mohit Patel, Marketing Specialist, Tailor Size Guide
Got a strip of paper and a ruler? That's all you need. Measure around your finger, or across the inside of a ring that already fits, and the calculator gives you your size in US, UK, EU and Japanese sizing. It takes about five minutes.
The short version
Your ring size is the inside circumference of the ring. A finger that measures 54.4 mm around is a US 7, a UK N½, and an EU 54. Each US size up adds about 2.5 mm of circumference. If you're between sizes, pick the bigger one.
Find your ring size
Enter a measurement in millimetres to see your size.
How to measure your finger with paper
You'll get a better number from a paper strip than from string. String stretches and twists, and both of those make your size read small. Cut a strip about 5 mm wide and 10 cm long.
- Wrap it around the base of the finger the ring is for. Snug, but not squeezing.
- Mark the overlap with a pen. Then slide the loop off over your knuckle. If it won't go, loosen it until it does.
- Measure the strip flat, from the end to your mark, in millimetres.
- Repeat twice more and use the largest of the three readings.
Want pictures for each step, or other methods? Our guide on how to measure ring size at home walks through five of them.
How to measure a ring you already own
Pick a ring that fits the same finger well. Not the finger next to it, and not the other hand. Lay it flat on a ruler and measure straight across the inside, from one inner edge to the other, through the centre. Don't include the metal. That's the inside diameter. Pick "A ring I own" in the calculator and enter it.
This is usually the most reliable way to size at home, because a metal ring doesn't stretch. A ring that's been resized or is slightly out of round can still throw it off, so measure across two directions and take the larger number.
When to measure (this matters more than people think)
Fingers change size through the day. Measure at the wrong moment and you can be off by half a size or more.
- Measure late in the day. Fingers are usually a little bigger in the evening than first thing in the morning.
- Measure at room temperature. Cold makes fingers shrink and heat makes them swell. Skip it right after a hot shower, a workout, or coming in from the cold.
- Watch for swelling. Salty food, alcohol, hot weather and pregnancy can all make fingers temporarily bigger.
- Check your knuckle. If your knuckle is much wider than the base of your finger, choose a size between the two so the ring gets on but doesn't spin.
- Use the right hand. Fingers on your dominant hand are often slightly larger. Measure the exact finger the ring is for.
Ring size chart: US, UK, EU and Japan
Find your inside circumference or diameter and read across.
| Circumference (mm) | Diameter (mm) | US | UK / AU | EU (ISO) | Japan |
|---|---|---|---|---|---|
| 44.2 | 14.07 | 3 | F | 44 | 4 |
| 45.5 | 14.49 | 3.5 | G | 45 | 5 |
| 46.8 | 14.91 | 4 | H | 47 | 7 |
| 48.0 | 15.28 | 4.5 | I | 48 | 8 |
| 49.3 | 15.70 | 5 | J½ | 49 | 9 |
| 50.6 | 16.10 | 5.5 | K½ | 51 | 10 |
| 51.9 | 16.51 | 6 | L½ | 52 | 12 |
| 53.1 | 16.92 | 6.5 | M½ | 53 | 13 |
| 54.4 | 17.32 | 7 | N½ | 54 | 14 |
| 55.7 | 17.73 | 7.5 | O½ | 56 | 15 |
| 57.0 | 18.14 | 8 | P½ | 57 | 16 |
| 58.3 | 18.54 | 8.5 | Q½ | 58 | 17 |
| 59.5 | 18.95 | 9 | R½ | 60 | 18 |
| 60.8 | 19.35 | 9.5 | S½ | 61 | 19 |
| 62.1 | 19.76 | 10 | T½ | 62 | 20 |
| 63.4 | 20.17 | 10.5 | U½ | 63 | 21 |
| 64.6 | 20.57 | 11 | V½ | 65 | 22 |
| 65.9 | 20.98 | 11.5 | W½ | 66 | 23 |
| 67.2 | 21.39 | 12 | X½ | 67 | 24 |
| 68.5 | 21.80 | 12.5 | Y½ | 68 | 25 |
| 69.7 | 22.20 | 13 | Z | 70 | 27 |
More detail in the full ring size chart, and country-by-country in US to UK, US to EU and US to Japan conversions.
Why sizes have different names in different countries
There's no single world ring size. Europe uses ISO 8653, which simply names the ring after its inside circumference in millimetres, so a 54 is 54 mm around. The UK, Ireland and Australia use letters from the British Standard, A to Z with half sizes. The US and Canada use numbers in quarter steps, where each whole size adds about 0.8 mm to the inside diameter. Japan uses its own numbered scale that runs roughly one number per millimetre of circumference.
All of them describe the same thing: the inside of the ring. That's why measuring in millimetres first and converting after is the safest route. It's also why "a 7" means nothing until you know which country's 7 it is.
Buying a ring as a surprise?
Borrow a ring they already wear on the right finger and measure its inside diameter. If that's not possible, trace the inside of the ring on paper and measure the circle. Still guessing? Go a little larger and check the jeweller offers free resizing. Most plain bands can be resized; eternity bands and some tungsten or titanium rings can't, so check before you buy.
Shopping for an engagement ring or wedding band? See our size guides for engagement rings and wedding rings.
Frequently asked questions
How do I find my ring size at home?
Wrap a thin strip of paper around the base of your finger, mark where it overlaps, and measure that length in millimetres. That is your finger circumference. Enter it in the calculator. Do it three times at the end of the day and use the largest reading.
Is it better to measure my finger or a ring I already own?
A ring you already own is usually more accurate, as long as it fits the same finger comfortably. Measure straight across the inside of the band, edge to edge, in millimetres. Paper and string can stretch or slip, which is why they often read a little small.
What if I'm between two ring sizes?
Go up to the larger size. A ring that's a touch loose can be fixed with a sizing bead or a quick resize. One that won't pass your knuckle can't be worn at all.
Do wide rings need a bigger size?
Usually, yes. A band wider than about 6 mm covers more of your finger and feels tighter than a thin band in the same size. Most jewellers suggest going up a quarter to a half size for wide bands.
What is the most common ring size?
Jewellers generally report that women's rings cluster around US 6 to 7 and men's around US 9 to 10. That's a rule of thumb, not a size you should guess with. Measure instead.
Are EU ring sizes the same as millimetres?
Yes. European sizes follow ISO 8653, which names a ring by its inside circumference in millimetres. A 54 is a ring with a 54 mm inside circumference, which is about a US 7.
Does the printable ring sizer work?
It can, but only if it prints at true size. Set your printer to 100% or 'actual size', then check the printed ruler against a real ruler before you trust it. A printer that scales to fit the page will throw your size off.
Standards behind this calculator
- ISO 8653:2016, Jewellery: Ring-sizes, definition, measurement and designation.The international standard that defines ring size as the inside circumference in millimetres. It's the basis for EU sizes in the chart.
- BS 6820, the British Standard for ring sizes.Defines the alphabetical UK sizes (A to Z, with half sizes) used in the UK, Ireland, and Australia.
- The US ring size scale.Each whole US size adds roughly 0.81 mm of inside diameter (about 2.55 mm of circumference). The calculator uses that step to convert your measurement.
The calculator gives a starting size. A jeweller's metal ring sizer is still the most accurate way to confirm it, especially for an expensive ring that's hard to resize.
Selling jewellery on Shopify?
Put a ring size chart right on your product pages. Tailor Size Guide adds per-product size charts so shoppers order the right size the first time.