π Ring Size Converter
Convert ring sizes between US, UK, EU, and Japanese systems.
Equivalent Ring Sizes
How to Use This Converter
Ring sizing has four major systems, and none of them agree with each other. Pick the system your size is in, enter the size, and this converter looks up the matching row in the standard chart and shows all four equivalents.
Choose the system your ring size comes in: US, UK, EU (millimeters of inside circumference), or Japan.
Enter the size. If you pick UK, a dropdown of standard UK sizes appears, since UK sizes are letters, not numbers.
Read off the equivalent sizes in all four systems. For EU and Japanese sizes that fall between chart rows, the converter picks the nearest row and tells you.
Treat every conversion as approximate: for engagement rings and wedding bands, get sized by a jeweler before ordering.
How the Four Systems Relate
There is no clean formula linking the systems, which is why this converter uses a lookup table instead of math. US sizes increase with finger diameter in roughly 0.8 mm steps. UK sizes run through the alphabet from H 1/2 upward, each full letter being about 1.25 mm of circumference. EU sizes are the most honest: they state the inside circumference in millimeters, so EU 51.9 means the ring\'s inner edge measures 51.9 mm around. Japanese sizes are a simple numbered scale where each step is about 1 mm of circumference.
Ring Size Conversion Chart
This is the standard chart the converter looks up. US sizes run from 4 to 13 in whole sizes:
Worked Example
A US size 6 looks up to UK L 1/2, EU 51.9 mm, and Japanese size 11. Going the other way, a ring stamped 59.5 inside the band is EU 59.5, which matches the US 9 row: UK R 1/2, Japanese 17. Notice the EU numbers climb by about 2.5 mm per US size, which means half a US size is roughly 1.25 mm of circumference.
Getting an Accurate Fit
Fingers change size through the day: they are smallest in the cold morning and largest in the warm evening, and they swell in heat and shrink in cold. Measure at room temperature in the evening for the truest reading. The ring should slide on with slight resistance and need a small tug to come off over the knuckle. Wide bands fit tighter than narrow ones, so size up a quarter to half size for bands 6 mm or wider. And when the ring matters, an engagement ring or a wedding band, skip the chart and visit a jeweler with a set of metal sizers: five minutes there beats a resize later.
Frequently Asked Questions
Are ring size conversions exact?
No, they are close approximations. The systems were invented independently: US sizes step by diameter, UK sizes use letter codes tied to circumference, EU sizes are the inside circumference in millimeters, and Japanese sizes count steps from a base. Rounding differences of a quarter size between charts are normal, which is why jewelers measure your finger directly for important rings.
How do I measure my ring size at home?
Wrap a strip of paper snugly around the base of the finger, mark where it overlaps, and measure the length in millimeters. That number is close to your EU size: divide the chart above by matching your millimeter reading to the EU column. Measure in the evening, when fingers are slightly larger, and do not measure cold hands, which shrink by up to half a size.
Why is there no single international ring size?
Each system grew out of a different jewelry tradition before global trade made standardization matter. The US scale came from diameter in inches, the UK from an alphabetical wheel, continental Europe from metric circumference, and Japan from its own numbered scale. Retooling every jeweler in the world was never worth it, so the charts coexist.
What is a US size 6 in UK?
A US size 6 converts to UK L 1/2, EU 51.9 mm, and Japanese size 11. This is one of the most common women's ring sizes, and it sits right in the middle of the conversion chart.
Should I size up for a wide band?
Yes. A wide band (6 mm or wider) covers more skin and fits more snugly than a thin band in the same nominal size. The usual advice is to go up a quarter to a half size for wide bands, and to try the actual ring on if possible, since comfort depends on the band's inner profile too.