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Ring Size Converter

Convert ring sizes between US, UK, EU/ISO, France, Germany, Japan, China, and Korea — or measure your finger's diameter or circumference to find your size instantly.

Inner diameter

17.32 mm

Inner circumference

54.41 mm

Ring sizes by system

UK / IE / AU

N½

EU / ISO

54

FR / IT / ES

14

Germany

17.3

Japan (号)

14

China / HK / TW

14

South Korea (호)

14

How to measure your ring size

  1. Paper-strip / string method: wrap a thin strip of paper or a piece of string snugly around the base of your finger, mark where it overlaps, lay it flat against a ruler, and read the length in millimeters — that is your inner circumference. Switch "Convert from" to "Inner circumference (measure)" and enter it.
  2. Measure an existing ring: lay a ring that already fits flat on a ruler and measure the inside opening edge-to-edge in millimeters — that is your inner diameter. Enter it under "Inner diameter (measure)".
  3. Measure at the end of the day, when your fingers are warm and at their largest. Cold fingers measure small.
  4. Measure the exact finger you will wear the ring on; the dominant hand usually runs slightly larger.
  5. If you fall between two sizes, choose the larger one. For wide bands (6 mm or more), go up a quarter to a half size.
  6. Measure two or three times and take the average — small differences in circumference change the size.

Ring size conversion chart

Ø (mm)Circ (mm)US / CanadaUK / IE / AUEU / ISOFR / IT / ESGermanyJapan (号)China / HK / TWSouth Korea (호)
14.0544.143F½44414444
14.4545.403.5G½45514.5555
14.8646.684H½47715777
15.2747.974.5I½48815888
15.7049.325J½49916999
16.1050.585.5K½511116111111
16.5151.876L½521216.5121212
16.9253.166.5M½531317131313
17.3254.417N½541417.3141414
17.7355.707.5O½561618151515
18.1456.998P½571718161616
18.5458.258.5Q½581818.5171717
18.9559.539R½602019191919
19.3560.799.5S½612119202020
19.7662.0810T½622219.8222222
20.1763.3710.5U½632320232323
20.5764.6211V½652520.6242424
20.9865.9111.5W½662621252525
21.3967.2012X½672721.4262626
21.7968.4612.5Y½682822272727
22.2069.7413Z½703022.2272727
World Calendars ConverterShoe Size Converter

Ring size converter. Find your size from a mm measurement or convert across US, UK, EU/ISO, Japan, China and Korea.

A ring size converter turns an inner diameter or circumference in millimeters into a ring size, then shows the matching size in every national system. Enter a measurement to discover your size, or pick a known size to read its equivalents.

What Is a Ring Size Converter?

There is no single global ring standard, so the same finger is a US 7, a UK N½, an EU/ISO 54, a Japan 14, and a German 17.3 all at once. To pin those scattered codes to one reality, you need the two physical numbers a jeweler actually measures — the inner diameter and inner circumference of the band in millimeters — and a way to read every national size off them. That is the job here: enter a measured inner diameter or circumference and it returns your size, or pick a size you already know and it shows the equivalents everywhere.
The split exists because each region built its scale on a different physical reference. The EU/ISO system (ISO 8653:2016) just states the inner circumference in millimeters, so an ISO 54 ring has a 54 mm circumference. France, Italy and Spain take that same circumference and subtract 40, turning ISO 54 into a French 14. Germany ignores circumference and uses the inner diameter in millimeters, so a 17.3 mm finger is a German 17.3. The US and Canada count in fixed steps of 0.81 mm of diameter, while the UK, Ireland and Australia use letters A to Z, with each division worth 1.25 mm of circumference. Japan, China, Hong Kong, Taiwan and Korea share one numeric index that climbs about a third of a millimeter of diameter per step.
Because every scale traces back to the same finger, two physical numbers tie them together: the inner diameter and the inner circumference, related by circumference = π × diameter. A 17.3 mm inner diameter is a 54.4 mm circumference, and that one finger is a US 7 worldwide. This converter anchors on those two measurements and reads every system off the same lookup table, so a Pandora 54 (Pandora uses EU/ISO sizing) and a Japanese 14 line up on the row a real jeweler's mandrel would give you.

Ring Size Conversion Chart (US, UK, EU/ISO, Japan & mm)

US / CAInner Ø (mm)Circ (mm)UK / AUEU/ISO (Pandora)FR / IT / ESGermanyJapan / China / Korea
515.749.3J½499169
616.551.9L½521216.512
6.516.953.2M½53131713
717.354.4N½541417.314
7.517.755.7O½56161815
818.157.0P½57171816
8.518.558.2Q½581818.517
919.059.5R½60201919
1019.862.1T½622219.822
1120.664.6V½652520.624

The Math Behind Ring Sizing

C=π×dC = \pi \times d
  • CC = Inner circumference of the ring in millimeters
  • dd = Inner diameter of the ring in millimeters
  • π\pi = Pi, approximately 3.14159
Ring sizing rests on one geometric fact: the inside of a ring is a circle, so its circumference and diameter are tied together by C = π × d. Measure either one and you have the other. A 17.3 mm inner diameter gives a circumference of 17.3 × π ≈ 54.4 mm, and dividing back, 54.4 ÷ π ≈ 17.3 mm. Every national scale is then layered on top of those two numbers.
The per-system rules, drawn from ISO 8653:2016 and the documented national conventions, are:
EUISO=round(C)EU_{ISO} = \text{round}(C)
FR/IT/ES=EUISO−40FR/IT/ES = EU_{ISO} - 40
DE=dDE = d
dUS=0.8128×sUS+11.63d_{US} = 0.8128 \times s_{US} + 11.63
The EU/ISO size is simply the inner circumference in millimeters rounded to a whole number, which is why Pandora, built on EU sizing, labels a 54 mm ring as size 54. France, Italy and Spain subtract 40 from that circumference. Germany reports the inner diameter directly. The US scale steps by 0.8128 mm of diameter (0.032 inch) per whole size, the UK adds one letter for every 1.25 mm of circumference from a baseline of C = 40 mm at size C, and the shared Asian index used by Japan, China, Hong Kong, Taiwan and Korea climbs about a third of a millimeter of diameter per step. Because the systems were each rounded independently, not every size has a clean whole-number twin in another system, so the converter snaps to the nearest row and flags an approximate match.

Ring Size Conversion Examples

US 7 across every system

A US 7 is the most-searched conversion because it sits near the average woman's size. It maps to an inner diameter of 17.3 mm and an inner circumference of 54.4 mm. In other systems that is UK N½, EU/ISO 54 (the same number Pandora uses), France/Italy/Spain 14, Germany 17.3, Japan 14, China/Hong Kong/Taiwan 14, and South Korea 14. So if a US shop has you at a 7 and a Japanese brand lists sizes in 号, you order a 14.

I measured 54.4 mm circumference — what size?

Say you wrapped a paper strip around your finger and it read 54.4 mm. Entered in circumference mode, the converter divides by π to get a 17.3 mm inner diameter and lands exactly on the US 7 row: UK N½, EU/ISO 54, France 14, Germany 17.3, Japan 14, Korea 14. If your strip read 52 mm instead, that is between rows: it divides to about 16.55 mm and snaps to the nearest, a US 6 (EU 52, Japan 12), marked with a ~ to show it is the closest match rather than an exact one.

Pandora 52 to US, Japan and the rest

Pandora sizes are EU/ISO sizes, so a Pandora 52 is an ISO 52, meaning a 52 mm inner circumference and a 16.5 mm inner diameter. Pick EU/ISO 52 in the converter and you get US 6, UK L½, France 12, Germany 16.5, and Japan/China/Korea 12. This clears up the most common brand confusion: a Pandora 52 is not a US 52, it is a US 6.

US 10 for a man's wedding band

Men's sizes cluster higher, around 9 to 11, and a US 10 is a frequent wedding-band size. It corresponds to a 19.8 mm inner diameter and a 62.1 mm circumference, which reads as UK T½, EU/ISO 62, France 22, Germany 19.8, and Japan/China/Korea 22. Remember a wide band fits tighter, so for a 6 mm-plus band consider going up to a US 10.5 (EU 63).

Tips for Getting the Right Ring Size

  • Measure at the end of the day. Fingers are smallest in the cold morning and fullest by evening, swinging up to a quarter size, so an evening measurement is the safest bet for a ring you will wear all day.
  • When you are between two sizes, order the larger one. A jeweler can usually size a ring down more easily than up, and a band that is a hair loose beats one that will not pass the knuckle.
  • Account for band width. A wide band of 6 mm or more sits tighter against the finger than a thin band, so add a quarter to a half size for chunky or stacked rings.
  • Match the measurement mode to your method. A paper strip gives inner circumference (enter 38 to 78 mm); a ring laid flat gives inner diameter (enter 12 to 25 mm). Mixing them up creates a roughly threefold error because circumference is π times the diameter.
  • Treat any ~ result as an approximate match, not a guarantee. Sizes rarely line up perfectly across systems, so for an engagement ring or a gift, confirm the size with the jeweler or order a free sizing kit before you buy.
  • For a surprise proposal, borrow a ring she already wears on the correct finger and measure its inner diameter, or trace the inside circle on paper. Confirm which hand and finger, since the dominant hand runs slightly larger.

Frequently Asked Questions About Ring Sizes

How do I measure my ring size at home?

Wrap a thin strip of paper or string snugly around the base of your finger, mark where it overlaps, and measure the length in millimeters with a ruler — that is your inner circumference. Or lay a ring that fits flat and measure the inside diameter edge to edge. Enter either number in the measurement mode above to get your size.

What is my Japanese ring size if I am a US 7?

A US 7 is a Japanese size 14 (written 14号). Both correspond to a 17.3 mm inner diameter and a 54.4 mm inner circumference. Japan, China, Hong Kong, Taiwan and Korea share the same numeric scale, so a US 7 is a 14 in all of them. Note some Japanese retailers number 号 in a slightly different way, so confirm against the shop's own chart if it lists millimeters.

What is my Korean ring size (호) if I am a US 7?

On the shared Asian scale this converter uses, a US 7 is a Korean 14. Be aware that two Korean conventions exist: some shops treat 호 as a diameter index like Japan, while others quote 호 as the inner circumference in millimeters (so a 호 54 means 54 mm). Because the labels can clash, always confirm whether the seller lists a millimeter measurement next to the 호 number.

What is my Pandora ring size?

Pandora uses EU/ISO sizing, where the size equals the inner circumference in millimeters. So a Pandora 54 has a 54 mm circumference and equals a US 7, and a Pandora 52 equals a US 6. Pick EU/ISO (Pandora) in the converter, or enter your circumference in mm, to see the Pandora number and its equivalents.

Is ring size the same for men and women?

Yes — ring size is unisex, defined purely by the finger's circumference, with no separate male or female scale. A men's size 9 and a women's size 9 share the identical inner diameter; only the averages differ (women US 5 to 7, men US 9 to 11).

How accurate is this ring size converter?

The conversions follow ISO 8653:2016 and the documented national rules, so they match a jeweler's chart to the nearest standard size. Accuracy then depends on your measurement: a careful paper-strip or existing-ring reading is reliable to about a quarter size. Because manufacturers round differently, treat any ~ result as the closest match and confirm with the jeweler for an engagement ring.

What should I do if I'm between two ring sizes?

Order the larger size. A loose ring can be resized down or fitted with a sizing bead, but one that won't pass the knuckle can't be saved. This matters even more for wide bands, which fit tighter — go up a quarter to a half size.

How do I measure the size of a ring I already own?

Lay the ring flat and measure straight across the inside of the band, edge to edge through the center, in millimeters — that is the inner diameter. Enter it in diameter mode. If the ring has gone slightly oval from wear, measure the narrowest and widest points and average them for a truer figure.

What is the difference between EU/ISO, German and French ring sizes?

They describe the same finger three ways. EU/ISO is the inner circumference in millimeters (ISO 54 = 54 mm). France, Italy and Spain subtract 40 from that circumference (so ISO 54 = French 14). Germany uses the inner diameter in millimeters instead (about 17.3 for that same ring). The converter shows all three at once so you never have to do the arithmetic.

Is this ring size converter free to use?

Yes, the converter is free, runs in your browser, and needs no sign-up. Enter a measurement or pick a known size and it instantly shows your size across US, UK, EU/ISO (Pandora), France, Germany, Japan, China, Hong Kong, Taiwan and Korea, along with the inner diameter and circumference in millimeters.

What does ring size mean in mm — diameter or circumference?

It can be either, depending on the country. EU/ISO and French sizes are based on the inner circumference in millimeters, while German sizes are the inner diameter in millimeters. The two are linked by circumference = π × diameter, so a 17.3 mm diameter is a 54.4 mm circumference. This converter reports both for every result.

Ring Sizing Terms Explained

Inner diameter

The straight-line distance across the inside of the ring band, edge to edge through the center, measured in millimeters. It is the physical reference Germany uses directly as its size number.

Inner circumference

The distance around the inside of the ring, measured in millimeters and equal to π times the inner diameter. EU/ISO ring sizes are simply this circumference rounded to a whole number.

ISO 8653

The international standard that defines ring sizes as the inner circumference in millimeters. It is the basis for the EU/ISO scale and for brands such as Pandora that label rings by circumference.

号 (gō)

The Japanese ring size unit, a whole number on the shared Asian scale. A Japanese 14号 corresponds to a US 7 and a 17.3 mm inner diameter.

호 (ho)

The South Korean ring size unit. On the common Asian scale it tracks the Japanese number, though some Korean retailers quote 호 as the inner circumference in millimeters instead, so it is worth confirming which convention a shop uses.

Comfort fit

A band style with a rounded, domed inside surface that slides over the knuckle more easily, so comfort-fit rings often feel about a quarter to a half size looser than a flat band of the same labeled size.

Approximate match (~)

A flag shown when a measurement falls between standard rows or a size has no exact twin in another system. The converter snaps to the nearest size and marks it with ~ so you know to confirm rather than assume an exact fit.

Content verified by the Smart Calculators Team