Ring size chart

How the sizes convert

ISO 8653 defines a ring size as the inside circumference in millimeters, which is the EU column. Every other system is a set of steps on top of that.

• US and Canada: size 0 is 11.63 mm across the inside, and each whole size adds 0.032 inches, or 0.81 mm. A size 6 is 16.5 mm, the same as on GIA's chart.
• UK and Australia: letters follow British Standard 6820, with 1.25 mm of circumference per letter and C at 40 mm. That puts M at 52.5 mm, between a US 6 and 6½, which is why many charts pair M with a 6.
• Japan: size 1 is 13.00 mm across and each size adds a third of a millimeter, as in Niwaka's size table.
• Switzerland, Italy and Spain: the size is the circumference minus 40, so Swiss 12 is EU 52.

The chart rounds EU, Japanese and Swiss sizes to the nearest whole size and UK sizes to the nearest half letter. Shops round differently and can disagree by half a size, so ask which scale a jeweler uses before you order.

How to measure your ring size at home

1. Measure a ring that fits. Use one from the same finger, since the left ring finger is typically about half a size smaller than the right for right handed people. Lay a ruler across the inside at its widest point and find that number in the inside column, or use the on-screen ring sizer.
2. Or print the paper sizer. Print at 100%, check the 50 mm line with a ruler, then cut out the strip.
3. Wrap it at the base of your finger, printed side out, snug but loose enough to slide over your knuckle. For most people the knuckle is the widest part of the finger.
4. Mark where the strip meets its end, lay it flat and read your size at the mark.
5. Measure twice, at different times of day. Fingers shrink in the cold and swell in the heat.
6. Size up when unsure. GIA says wide bands usually need a bit more room, and that it is easier to take metal out of a ring than to add it.

GIA also warns that paper can tear and string can stretch, so treat a paper result as a starting point and have a jeweler confirm your size before you buy.