Ring Size Converter

About the Ring Size Converter

Convert a ring size between the US & Canadian numbers, UK, Irish and Australian letters, the EU/ISO circumference in millimetres, Swiss, Italian and Spanish sizes, the German and Dutch diameter, and the Japanese and Indian scales. Start from the size you know, the inside diameter of a ring that fits, a paper-strip or string measurement of your finger — or lay a ring on your screen after calibrating it with any bank card.

Every result shows the nearest size in each system and the inner circumference that size stands for, so you can see how close the match is. Indian sizes come from one published jeweller’s chart (Indian jewellers each use their own) and Japanese sizes from the customary Japanese rule, and both are flagged as such.

Common uses

• Buying a ring online from a shop in another country — a US size from a UK jeweller, an EU size from an Italian brand.
• Finding your size at home with a strip of paper, a piece of string or a ring that already fits.
• Choosing a surprise engagement ring from a borrowed ring’s inside diameter.
• Ordering from an Indian jeweller: give the size and the circumference in mm.

How the systems are defined

Every system describes the inside of the ring:

• EU / ISO 8653: the inner circumference in mm — size 54 is 54 mm around. Used in France, Belgium, Austria, the Nordic countries and most of continental Europe.
• US & Canada: size 0 is 0.458 in (11.63 mm) across and each size adds 0.032 in (0.8128 mm), in quarter sizes; so the circumference is about 36.5 + 2.55 × size mm.
• UK, Ireland, Australia, New Zealand (BS 6820): letters with half sizes, 1.25 mm of circumference per letter, from A = 37.5 mm (C = 40 mm) to Z = 68.75 mm, then Z+1, Z+2 …
• Switzerland, Italy, Spain: the circumference minus 40 mm — size 14 is 54 mm.
• Germany, Netherlands: the inner diameter in mm; Russia rounds it to half a millimetre.
• Japan (customary 号): 13 mm across for size 1 and ⅓ mm more per size; the Japanese standard JIS S 4700 uses the ISO circumference instead.

Indian ring sizes

Indian jewellers do not share one ring-size scale: each publishes its own chart, and the charts can disagree by a size or more. This converter uses ORRA’s published chart for sizes 7 to 26 (size 12 is 54.4 mm around, 17.3 mm across) and says so in the result. Before you order, ask your jeweller for their chart or give them the circumference in millimetres.

Measuring on screen

A web page does not know how big its pixels are, so the on-screen sizer first asks you to match an outline to a bank card — every bank, debit and most ID cards are 85.60 × 53.98 mm (the ID-1 size of ISO/IEC 7810). The calibration is saved for this screen in this browser. Then match the circle to the inside edge of a ring. A 0.1 mm error in the diameter is about ⅛ of a US size, so check against a second ring or a ruler if you can.

Limitations

• A conversion gives the nearest size; real rings vary with the band width, the profile (comfort-fit bands feel larger) and the jeweller’s mandrel. Wide bands fit tighter.
• Indian and Japanese results come from one published chart and the customary rule; other jewellers can differ.
• The on-screen sizer is only as accurate as its calibration and how well the ring is lined up. It is a guide, not a replacement for a jeweller’s ring gauge.
• Fingers change size with temperature and the time of day; measure more than once.

Privacy

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