Ring Size Converter
Know your ring size in one system? Get it instantly in every other system, plus a full chart and measuring guide.
How to measure your ring size at home
Existing ring: measure the inner diameter of a ring that already fits (in millimeters, straight across the hole), then select "Inner Diameter (mm)" above.
String or paper strip: wrap a strip snugly around your finger, mark where it overlaps, measure that length in millimeters, then select "Circumference (mm)" above.
About this tool
What this tool does
Enter a ring size in whatever system you have — US/Canada number, UK/Australia letter, or a direct diameter or circumference measurement in millimeters or inches — and it converts to every other system at once, including the EU (ISO) size. A full reference chart and an at-home measuring guide are built right in.
Who it's for
Anyone buying jewelry from an overseas retailer who lists sizes differently than they're used to, someone resizing an inherited or gifted ring, or a jeweler double-checking a customer's measurement against multiple regional standards.
How to use it
- Pick what you already know from the "Convert From" dropdown — US size, UK/Australia letter, or a diameter/circumference measurement.
- Enter the value (or pick the letter size), and every other system updates instantly below.
- No ring to measure from? Use the at-home guide: measure an existing ring's inner diameter, or wrap a strip of paper or string around your finger and measure the overlap point.
- Click "View Full Size Chart" to browse every size side by side, or Copy Results to save your conversion.
Real-world uses
Converting a UK ring size to US before ordering from an American jeweler, checking what EU size corresponds to a US 7, or figuring out your size from a ring you already own without visiting a jeweler.
Frequently asked questions
How accurate is measuring with a string or paper strip?
It's a solid estimate, usually within half a size, but ring width, finger shape, and time of day (fingers swell slightly in heat) can shift the result. For anything permanent or expensive, a jeweler's metal ring sizer is more precise.
What does the EU ring size number actually mean?
Most of continental Europe uses the ISO 8653 standard, where the size number is simply the inner circumference in millimeters rounded to the nearest whole number — a EU size 54 ring has a 54mm inner circumference.
Why do UK sizes use letters instead of numbers?
The UK and Australia both use an alphabetical scale (A through Z, with half sizes like "M½") based on the inner circumference, a system that predates the numeric scales used in the US and Canada.
Can I convert a size for a wide band the same way?
Not quite as-is — wider bands (over about 6mm) typically need to be sized slightly larger than a thin band, since a wide band touches more of the base of your finger where it's less flexible. Ask your jeweler about a "comfort" adjustment for wide styles.
Does ring size differ between fingers?
Yes, often by a full size or more — your dominant hand is typically slightly larger, and each finger has its own size. Always measure the specific finger the ring will be worn on.