Are UK and US ring sizes the same?

No. UK sizes use letters (e.g. L, N, Z+1), while US sizes use numbers (e.g. 6, 7, 9.5). A UK L is approximately US 6, but always confirm with a jeweler before ordering, since brands round slightly differently.

Why does a UK letter sometimes map to a US half size?

Both systems measure the same inner circumference in millimeters, but they step through it at different intervals. UK letters increase in smaller increments than US whole numbers, so a letter often lands between two US sizes and gets rounded to the nearest half.

How do I measure my ring size at home?

Wrap a thin strip of paper around your finger, mark where it overlaps, and measure the length in millimeters. That length is your inner circumference; use the chart on this page to find the closest UK and US sizes.

Does this cover half UK sizes like L½?

Yes. The dropdown and chart include every half-letter step from A to Z+3, which covers the full adult ring size range used by UK jewelers.

What is the difference between circumference and diameter here?

Circumference is the distance around the inside of the ring; diameter is the straight-line width across the inside. Diameter equals circumference divided by pi. Both are shown so you can verify a size against a physical ring or a printable sizer.

UK Ring Size to US Ring Size Converter

Select a UK ring size letter and instantly see the equivalent US ring size, plus inner circumference and diameter in millimeters.

UK to US Ring Size

UK Ring Size

Full UK to US Ring Size Chart

US size is the nearest half size for each UK letter's inner circumference.

UK Size	US Size	Circ (mm)	Diam (mm)

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Summary

This tool converts UK ring sizes, which use a letter scale from A to Z+3, into their US numeric equivalents. Both scales are derived from the same inner circumference measurement in millimeters, so the converter maps each UK letter to the nearest US half size and shows the exact circumference and diameter behind that result. Enter or select a UK letter and the US size, along with the mm measurements, appears right away.

How it works

Select a UK ring size letter (A to Z+3, including half sizes) from the dropdown.
The tool converts the letter to an inner circumference in millimeters.
That circumference is mapped to the nearest US ring size.
Inner circumference and diameter are shown alongside the US size.
Browse the full chart on the right to compare every UK to US pairing at once.

Use cases

Order a ring from a US jeweler when you only know your UK size.
Buy a ring as a gift for someone who gave you their UK size.
Check the US equivalent before ordering a ring online from an American retailer.
Compare ring dimensions in mm when resizing a ring across regions.
Convert a size printed inside an old UK ring to shop for a US replacement.

Frequently Asked Questions

Last updated: 2026-07-14 · Reviewed by Nham Vu