Converters
Ring Size Chart & Converter
Convert between US, UK, European and Japanese ring sizes, turn a finger measurement into a size, or measure a ring you already own.
Wrap a strip of paper or non-stretchy string round the base of the finger, mark where it overlaps, lay it flat and measure the length in millimetres.
Ring size conversion chart
Inner measurements of the ring. EU sizes follow ISO 8653 (inner circumference in mm); UK letters follow BS 6820 (C = 40 mm, 1.25 mm per letter).
| US / Canada | UK / AU | EU / ISO | Japan | Diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 14.1 mm | 44.2 mm |
| 3½ | G½ | 45 | 5 | 14.5 mm | 45.5 mm |
| 4 | H½ | 47 | 7 | 14.9 mm | 46.8 mm |
| 4½ | I½ | 48 | 8 | 15.3 mm | 48.0 mm |
| 5 | J½ | 49 | 9 | 15.7 mm | 49.3 mm |
| 5½ | K½ | 51 | 10 | 16.1 mm | 50.6 mm |
| 6 | L½ | 52 | 12 | 16.5 mm | 51.9 mm |
| 6½ | M½ | 53 | 13 | 16.9 mm | 53.1 mm |
| 7 | N½ | 54 | 14 | 17.3 mm | 54.4 mm |
| 7½ | O½ | 56 | 15 | 17.7 mm | 55.7 mm |
| 8 | P½ | 57 | 16 | 18.1 mm | 57.0 mm |
| 8½ | Q½ | 58 | 18 | 18.5 mm | 58.2 mm |
| 9 | R½ | 60 | 19 | 18.9 mm | 59.5 mm |
| 9½ | S½ | 61 | 20 | 19.4 mm | 60.8 mm |
| 10 | T½ | 62 | 21 | 19.8 mm | 62.1 mm |
| 10½ | U½ | 63 | 22 | 20.2 mm | 63.3 mm |
| 11 | V½ | 65 | 24 | 20.6 mm | 64.6 mm |
| 11½ | W½ | 66 | 25 | 21.0 mm | 65.9 mm |
| 12 | X½ | 67 | 26 | 21.4 mm | 67.2 mm |
| 12½ | Z | 68 | 27 | 21.8 mm | 68.5 mm |
| 13 | Z+1 | 70 | 29 | 22.2 mm | 69.7 mm |
| 13½ | Z+2 | 71 | 30 | 22.6 mm | 71.0 mm |
How the sizes are defined
US and Canada: size 0 is 11.63 mm (0.458 in) across the inside, and each whole size adds 0.8128 mm (0.032 in) of diameter — about 2.55 mm of circumference. UK, Ireland and Australia: letters A–Z in half sizes, each letter 1.25 mm of circumference, with C at 40 mm (BS 6820:1987); beyond Z come Z+1, Z+2 and so on. Europe: ISO 8653:2016 simply names the size after the inner circumference in millimetres, so size 54 is 54 mm round. Japan: the customary scale starts at 13 mm diameter for size 1 and adds ⅓ mm per size. Switzerland and Italy use the circumference minus 40.
Because the systems use different steps, neighbouring columns never line up exactly — a conversion is the nearest size, not an identity. Jewellers’ printed tables can differ from each other by up to half a size for the same reason, so for an expensive ring, confirm with the jeweller’s own ring gauge.
Everything is calculated in your browser; measurements and calibration stay on this device.
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Frequently asked questions
How do ring size systems differ?
They measure the same thing — the inside of the ring — in different steps. US and Canadian sizes add 0.8128 mm of inner diameter per whole size, starting from 11.63 mm at size 0. UK and Australian letters step by 1.25 mm of circumference, with C at 40 mm (BS 6820). ISO 8653, used across Europe, names each size after the inner circumference in millimetres. Japan’s customary scale starts at 13 mm diameter and adds a third of a millimetre per size.
What size is a US 7 ring in UK, EU and Japanese sizes?
A US 7 has an inner diameter of about 17.3 mm and a circumference of about 54.4 mm. That is UK N½, EU/ISO 54 and Japanese 14. Because the systems use different steps, the equivalents are always the nearest size rather than an exact match, and printed tables can differ by half a size.
Why do I need to calibrate before measuring a ring on screen?
Web pages measure in CSS pixels, and the physical size of a CSS pixel depends on the screen, its resolution and the browser’s zoom. Matching the outline to a real bank card — a standard ISO/IEC 7810 ID-1 card, 85.60 mm wide — tells the page how many pixels make a millimetre on your display. Without that step an on-screen circle can easily be 10–20% off, which is several ring sizes.
How do I make sure the printable ring sizer prints at the right size?
Choose 100% or “Actual size” in the print dialog and turn off “Fit to page”, “Shrink to fit” or “Scale to fit”. Then measure the 100 mm ruler at the top of the sheet with a real ruler, or lay a bank card along it. If 100 mm does not measure 100 mm, the circles and the strip are wrong too, so fix the print settings and print again.
Should I choose the larger size if I am between sizes?
Usually yes. The ring must pass over the knuckle, fingers swell in heat and later in the day, and wide bands (about 6 mm and over) fit tighter than narrow ones, so jewellers commonly suggest half a size up for them. If the knuckle is much larger than the base of the finger, measure both and ask a jeweller about a size that clears the knuckle.
Is the string method accurate?
It is a reasonable estimate, but string can stretch or twist and it is easy to pull too tight. Paper strips are more reliable. Measure two or three times, at the end of the day and at normal room temperature, and never with cold hands. For an engagement or wedding ring, confirm the result with a jeweller’s ring gauge before a ring is sized or engraved.
About this tool
This ring size chart converts between the main sizing systems in use today: US and Canadian numeric sizes in quarter steps, UK, Irish and Australian letters with half sizes, European sizes under ISO 8653, and Japanese sizes. Each row also lists the ring’s inner diameter and inner circumference in millimetres, the two physical measurements every system is built on. Alongside the chart are three ways to find a size you do not know yet: type a measurement, measure a ring on screen, or print a sizer.
The conversions follow published definitions rather than a copied table. ISO 8653:2016 designates a ring by its inner circumference in millimetres. The North American scale starts at 11.63 mm (0.458 in) inside diameter for size 0 and adds 0.032 in (0.8128 mm) per whole size — though the US Bureau of Standards noted as early as 1921 that American ring gauges differed slightly from maker to maker. British Standard BS 6820:1987 sets UK letters 1.25 mm of circumference apart with letter C at 40 mm. Japan’s customary scale, still used alongside the ISO-based JIS S 4700, starts at 13 mm diameter for size 1 and adds a third of a millimetre per size. Because the steps differ, a converted size is the nearest one available, and printed jewellers’ tables can disagree with each other by half a size.
Measuring a ring on screen only works if the page knows how big your pixels are, so the tool starts with a calibration step: you hold a bank or ID card against the screen and adjust an outline until it matches the card, which the ISO/IEC 7810 ID-1 standard fixes at 85.60 × 53.98 mm; on a phone you match the short edge, since a card is wider than most phone screens. After that, the circle you drag over your ring is drawn at true size. The calibration is saved only in this browser, and the page asks for it again if the zoom level changes.
The printable ring sizer is a one-page PDF for A4 or US Letter with 21 true-size circles from US 3 to 13 and a cut-out strip marked in quarter sizes. It includes a 100 mm ruler and a 4 inch ruler to confirm that the sheet printed at 100%, because a printer set to “fit to page” typically shrinks everything by a few percent — enough to put a ring half a size or more out. Whichever method you use, measure at the end of the day with warm hands, and have a jeweller confirm the size before an expensive ring is resized or engraved.