Ring Size Converter
Have a measurement or know one size? Convert an inner diameter, a finger circumference or a listed size into approximate international equivalents.
Enter your reading and choose Convert.
Your closest reference size
- Equivalent inner diameter
- Equivalent inner circumference
Approximate reference conversion. Check the seller’s chart before ordering.
Compare every half sizeAcross or around?
One inch is 25.4 mm. For circular geometry, circumference = diameter × π. For example, 54 mm around is approximately 17.19 mm across. This conversion does not establish how a real finger will fit a rigid ring.
How this ring size converter chooses a row
Measurements match the closest inside diameter in our US 3–15 half-size table. US, UK and Japanese inputs must be listed reference sizes. EU input is interpreted as circumference in millimetres. We retain the entered measurement rather than replacing it with the selected row’s nominal diameter.
UK and Japanese equivalents use the published mappings; missing entries stay blank. EU is a rounded circumference reference. A number outside the table range produces a message instead of a substituted boundary size.
Sources: GIA ring sizing reference and Peter Stone diameter reference. Read the conversion method and limitations.
Ring Size Converter FAQs
Answers about this method, its inputs and its limits.
Check the conversion chartRead the measurement methods, sources and limitations behind this tool.
Method and sourcesWhat ring size is a 54 mm circumference?
A 54 mm circumference is about 17.19 mm in equivalent diameter, using circumference ÷ π. In this reference it is closest to US 7, UK N and JP 14, with EU approximately 54. Keep the original 54 mm reading when checking a retailer’s chart.
Is 17 mm a ring size or a finger circumference?
Specify what you measured. A 17 mm inner diameter is closest to US 6.5 in this half-size reference. A 17 mm circumference would be outside its range. The distance across an opening and the distance around a finger are different inputs.
Can I convert ring measurements in inches?
Yes. Select inner diameter or circumference, choose inches and enter the reading. The converter multiplies inches by 25.4 before looking up the nearest diameter.
Why does a UK or Japanese size sometimes show a dash?
A dash means this source does not provide an equivalent for that row. We preserve missing mappings instead of inventing a size. Try a measured inner diameter and check the seller’s chart.
Does the converter measure my finger?
No. It converts a number you already know or measured. For a screen-based visible-width estimate, use finger mode on the homepage. That method does not measure circumference.