Ring Size Reference & Converter

Ring Size enquiry form 1

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US size
UK size
JP size
EU size
We usually provide ring sizes in millimeters or fractions of an inch of diameter. Make sure you use the internal (int) diameter of the ring if given. Since ancient rings are not always made completely round we sometimes provide a measurement such as 16 x 18 mm int diameter. In this case take the average internal diameter (16+18)/2=17 and enter it in the converter to find the equivalent ring size.

Ring Size Scales

There are a number of different ring size scales of measurement used in the world. These are the main ones.

British Standard(s).
In the UK, sizes are measured by alphabetical letter A - Z although it is often necessary to go above size Z by appending ' Z+1, Z+2, Z+3,' etc. The sizes are evenly spaced with half sizes (eg. M½ ) in between.   More
American Sizes.
The American (US) sizes are based on numbers 1 - 15 or so also with half and quarter sizes (eg. 6½ ). One half size US is roughly equivalent to one whole size UK.   More
Japanese Sizes.
This is a numerical system based on ring diameter - one division being one third of a millimeter, startiing with size 1 at 13 mm inside diameter. Small and medium ring sizes correspond closely with European ring sizes.
European Sizes.
The European ring sizes are based on the circumferential measurement of the ring in millimetres (eg: 53 ); The more general European system of ring sizes uses the inner circumference (in mm) minus 40., (eg: 13 ).
Metric Circumference.
The direct metric measure of the inside circumference of the ring is a straighforward and logical method that produces sizes in the range 40 to 76 or so. 1 mm divisions give a fair spacing of sizes and this system allows measurement of the finger without special gauges.
Metric Diameter.
Not such a useful measurement as the full range of ring sizes would fit between say 12 and 25 mm (½ & 1 inch) of internal diameter, but an acceptable method of communicating the size of an existing round ring provided it is measured to an accuracy better than ¼mm. Imperial measurements of similar accuracy (10/1000 inch) are also acceptable.

British Ring Size Standards

The generally used British Standard 1283:1945 was based on the "Wheatsheaf gauge and represented the sizes alphabetically. The divisions were based on the ring inside diameter in steps of 1/64 th inch (0.0156 inch = 0.397 mm).

In 1987 a new British Standard 6820 was introduced based on International Standard 8653 basing the ring size on metric circumference such that one (alphabetic) size division equals 1.25 mm of circumferential length. The new sizes were set to be very close to the old (1945) sizes (which rendered the circumference divisions to 1.247 mm). For a baseline, ring size C = 40 mm. circ.     see: Calculations   Back

American Ring Sizes.

At one time, the American inch differed slightly from the imperial inch and the U.S.A. ring size scale divisions were each 1/10 U.S. inch of circumference. American ring sizes were not revised with the inch and therefore do not relate exactly and simply with other systems: 1 size US = 2.60 mm of circumference.     see: Calculations   Back


There is no simple way to equate all the systems, but we provide a Size Convertor, and here are formulae for relating diameters (dia) and circumferences (circ) in inches (in) and metric (mm) and ring sizes ( for UK sizes equate A=1, B=2, etc. in the formulae): Top