# My Ring Size: ring size scales, formulas and worked sizes, one per line
# Source: the scale definitions and our own arithmetic, explained at https://myringsize.app/how-we-calculate/ (checked 2026-10-12). Sizes are the nearest on each scale; jewellers' charts differ by a few tenths of a millimetre.
# Format: kind | name | fact | page
Scale | US / Canada / Mexico | numeric sizes in quarter steps; inner diameter in mm = 11.63 + 0.8128 × size (one whole size is 0.032 in = 0.8128 mm of diameter, 2.55 mm of circumference; size 0 is 11.63 mm, 36.5 mm around) | https://myringsize.app/
Scale | UK / Ireland / Australia / New Zealand | letters A to Z with half sizes; since BS 6820:1987 each letter is 1.25 mm of inner circumference and size C is 40 mm, so circumference = 37.5 + 1.25 × (A = 0, B = 1 …), half sizes + 0.625 mm | https://myringsize.app/
Scale | EU / ISO 8653 | the inner circumference in millimetres (ISO 8653:2016); a size 54 ring is 54 mm around inside, 17.19 mm across | https://myringsize.app/
Scale | Japan / East Asia | the trade scale 号: size 1 is 13.0 mm inner diameter and each size adds 1/3 mm (size 14 = 17.33 mm); secondary sources disagree on whether JIS S 4700 numbers rings this way or by circumference, so this is the jewellers’ chart basis, not a quoted standard | https://myringsize.app/
Formula | Circumference and diameter | inner circumference = π × inner diameter; 16.5 mm across is 51.8 mm around | https://myringsize.app/
Example | US 7 | inner diameter 17.32 mm, circumference 54.4 mm; nearest UK N½, EU 54.5, Japan 14 | https://myringsize.app/ring-size-converter/
Example | UK L | circumference 51.25 mm, inner diameter 16.31 mm; nearest US 5¾ | https://myringsize.app/ring-size-converter/
Formula | Nearest size | a measurement is converted to a circumference, and each scale returns its nearest stocked step (US quarter sizes, UK half letters, EU half millimetres, Japan whole numbers) with the distance from exact in mm | https://myringsize.app/ring-size-converter/
Formula | Measuring with string | the length of a strip wrapped snugly round the finger is the inner circumference; 54 mm around is US 6¾ (about a 7; diameter 17.2 mm) | https://myringsize.app/how-to-measure-ring-size/
Formula | Knuckle rule | when the knuckle is larger than the base of the finger, use a circumference halfway between the two, so the ring passes the knuckle and does not spin | https://myringsize.app/how-to-measure-ring-size/
Example | Men’s range | US 8 to 12 is 18.1 to 21.4 mm across, 57 to 67.2 mm around; US 10 is 19.76 mm | https://myringsize.app/mens-ring-size-chart/
Example | Sizes in mm | US 6 = 16.51 mm across; UK L = 16.31 mm; EU 52 = 16.55 mm; Japan 12 = 16.67 mm | https://myringsize.app/ring-size-in-mm/
Formula | Printable sizer | each circle is drawn at the exact inner diameter of its US size (11.63 + 0.8128 × size mm); the strip is marked at each size’s circumference; a bank card (85.60 × 53.98 mm) checks the print scale | https://myringsize.app/printable-ring-sizer/
Reference | Average sizes | women US 6 to 7 and men US 9 to 10 are the sizes jewellers report selling most, with usual ranges of about US 5 to 8 and 8 to 12; these are trade figures, not a measured population survey | https://myringsize.app/average-ring-size/
Reference | On-screen sizer | the screen is calibrated by matching an outline to a bank card, 85.60 mm wide (ISO/IEC 7810 ID-1), which gives the pixels per millimetre; the circle is then drawn at a true diameter | https://myringsize.app/ring-sizer/
Example | Chart range | the chart runs US 3 to 15 in half sizes, 14.07 to 23.82 mm across | https://myringsize.app/