⚠ Important: For 100% Ring Size Accuracy, visit your local jeweler for an in-person measurement. All tools on this site are estimates only.
All Systems Explained

Ring Sizes — The Complete Guide

A comprehensive overview of how ring sizes work worldwide — from the numbers and letters used to mm measurements and how to convert between systems.

Ring sizes are standardised measurements that indicate the inner circumference or diameter of a ring. Different countries and regions have developed different standardised systems over time, which is why a ring labelled "size 7" (US) might be "size N" in the UK or "size 54" in France — all referring to the same physical measurement.

How Ring Sizes Are Determined

All ring sizing systems ultimately refer to the same underlying physical measurement: the inner circumference or inner diameter of the ring. The difference between systems is simply the unit and scale used to express that measurement:

  • US/Canada: Arbitrary numerical scale (3–14)
  • UK/IRE/AUS: Arbitrary alphabetical scale (A–Z+)
  • EU/French/German: Inner circumference in mm directly
  • Japan/China: Numerical scale loosely based on circumference
  • Swiss: Inner diameter in mm minus 40

Complete Ring Size Reference Table

USUKEUJapanSwissDiameter (mm)Circumference (mm)
3F444414.144.2
3.5G455514.545.6
4H46.576.514.946.8
4.5I488815.348.0
5J499915.749.3
5.5K50.51110.516.150.6
6L51.51211.516.551.9
6.5M53131316.953.2
7N54141417.354.4
7.5O55.51615.517.755.7
8P57171718.257.2
8.5Q58181818.558.2
9R59191918.959.3
9.5S61212119.461.0
10T62222219.862.2
10.5U63.52423.520.263.5
11V65252520.765.0
11.5W66262621.166.2
12X67.52827.521.567.5
12.5Y68.52928.521.968.8
13Z70303022.370.1
14Z+271313122.771.3

The Most Important Sizes to Know

Across all systems, these benchmark sizes cover the most commonly purchased rings:

Women's Average

US 6 · UK L · EU 51.5
16.5mm diameter · 51.9mm circumference
The most commonly sold women's size worldwide.

Men's Average

US 10 · UK T · EU 62
19.8mm diameter · 62.2mm circumference
The most commonly sold men's size worldwide.

Small Women's

US 5 · UK J · EU 49
15.7mm diameter · 49.3mm circumference
Common for petite frames and smaller hands.

Large Men's

US 12 · UK X · EU 67.5
21.5mm diameter · 67.5mm circumference
Common for large-framed men.

When in doubt about ring sizes: Provide the inside diameter or circumference in millimetres. These measurements are universally understood by jewellers worldwide and eliminate any ambiguity about which sizing system is being referenced.