Why ring sizes differ by country
Ring sizes are not measurements — they are country-specific scales. The US uses a numeric scale based on inner diameter, the UK and Australia use letters with half steps, while the EU and Japan are based on the inner circumference in millimetres. A comfortable US 7 is about a UK N½, EU 54, and JP 14. This calculator works from the true inner circumference so one measurement gives you every system.
Measuring your finger at home
Cut a strip of paper or string, wrap it around the base of the finger, mark where it overlaps, and measure that length in millimetres — that is your circumference. Measure in the evening when fingers are warm, and if you are between sizes choose the larger for comfort. Width of the band matters too: a wide band sits tighter, so size up half a size.
Reading circumference and diameter
Two numbers describe any ring: the inner circumference (the length around the inside) and the inner diameter (the distance across). They are linked by π, so diameter × π = circumference. Keep the millimetre values from this tool handy — they are the universal language every jeweller understands, regardless of the letter or number on a tag.
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- Five systems at once: US, UK / AU, EU, and JP ring sizes
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- Measure by circumference or inner diameter (mm, cm, or inches)
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- Live ring preview that scales to your exact inner diameter
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- Band-width option that sizes up for a comfortable wide-band fit
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- Reverse convert: enter any known size to see all equivalents (each scale keeps a sensible default)
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- UK and AU alphabetic sizes with half steps (e.g. N½)
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- Exact circumference and diameter in millimetres for printing
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- Copy any size to clipboard with one click
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- Printable ring size chart (US 4–13) with a one-tap Print button
