International Ring Size Converter

Online ring shopping breaks down at the size box — the US sells 6½, the UK sells L½, the EU prints 54 and Japan / Hong Kong prints 14. Pick the system you have, type the size (or your inner-finger circumference in mm) and the tool maps it to every other system at once, including the ISO 8653 international standard.

Measurement / size system Value

Equivalent sizes

Exact match

Inner circumference: —
Inner diameter: —
US / Canada: —
UK / AU / IE: —
Japan / Hong Kong / China: —
EU / ISO 8653: —

How to measure

Wrap a thin strip of paper or a piece of string around the base of your finger, mark where it overlaps, then measure the length in millimetres — that is your inner circumference. Measure in the evening (fingers are largest then); summer and winter sizes can differ by half a size.

Chart cross-referenced from published GIA, Tiffany, Blue Nile and Brilliant Earth international ring size charts. EU / ISO 8653 size equals the inner circumference in mm; Japan, Hong Kong and Mainland China share the same numeric scale. UK / AU / IE uses a letter scale.

Formula

Reference (units: mm): inner_circumference = π × inner_diameter EU / ISO 8653 ≈ inner_circumference (mm) US size ≈ (inner_circumference − 36.5) ÷ 2.55 Japan / HK ≈ numeric scale aligned to the US table

· Chart covers US 3 through 13 in half-size steps (21 rows): inner circumference 44–70 mm, UK F through Z½, JP / HK 4 through 27, EU 44–70.
· EU / ISO 8653 is literally defined as "inner circumference in mm" — measure the band circumference and you have your EU size. Japan, Hong Kong and mainland China share one numeric scale.
· US / Canada uses ¼ and ½ half-sizes. UK / AU / Ireland uses an A–Z letter scale with ½ steps (each letter ≈ 1.25 mm of circumference).
· How to measure: wrap a thin strip of paper or piece of string around the base of your finger, mark where it overlaps, then measure the length in millimetres — that is your inner circumference. Or measure the inner diameter of a ring that already fits, then multiply by π.
· Measure in the evening — fingers are typically at their largest then; summer and winter sizes can differ by half a size. Avoid measuring right after exercise, salty meals or cold water — they distort the reading.
· Source: cross-referenced from GIA, Tiffany & Co., Blue Nile and Brilliant Earth public ring-size charts. Individual brands may sit ±¼ size off — always confirm against the brand's own size chart before purchase.

Frequently asked

Which ring size system do shops in Hong Kong typically use?

Mainstream Hong Kong jewellers (Chow Sang Sang, Chow Tai Fook, Tse Sui Luen, Lukfook) use the "HK" numeric scale, which is identical to the Japanese / Chinese system — roughly 1 through 30, one number per integer step. International houses (Tiffany, Cartier, Bvlgari, Van Cleef) lead with US sizes and may list EU as a secondary. Wherever you shop, remember your inner circumference in mm — it's the ISO 8653 anchor every chart agrees on.

When is the best time of day to measure my finger?

Measure in the evening — fingers swell through the day and the evening size is closest to how a ring will sit during normal wear. Morning vs. evening can differ by ¼–½ a size. Avoid measuring right after exercise (fingers are engorged), a salty meal (water retention), cold water (vasoconstriction shrinks fingers) or in deep winter outdoors (can be a full size smaller). Measure the same finger two or three times and average.

I already own a ring that fits — can I size from that instead?

Yes — sizing from a ring that already fits is the most reliable method. Use a ruler or digital caliper to measure the inner diameter (the widest distance across the inside of the band) in mm, then pick "Inner diameter (mm)" in the tool and enter the number. Or trace the inside of the ring on paper and measure across the circle. Important: measure the inner diameter, not the outer — bands are typically 1.5–2 mm thick and measuring outside will over-estimate by roughly one full size.

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