Ring Size Letters to Numbers: Full Conversion Reference
A complete guide to converting between UK letter sizes and US number sizes, including EU measurements and diameter references.
Many people encounter ring sizes as letters when shopping online in the UK, Australia, or other Commonwealth countries, or as numbers when purchasing from US retailers. Converting between these systems can be confusing, especially when faced with a vintage ring engraved with a letter size or when ordering from international sellers. This complete reference guide maps every UK letter size to its US numeric equivalent, along with EU measurements and inner diameter in millimeters so you can always find the right fit.
Understanding how to convert letter to number ring sizes is essential for anyone shopping across borders or working with jewelry that uses different sizing conventions. Whether you're a jeweler, a shopper, or simply someone who inherited a ring with an unfamiliar size marking, this guide provides the definitive reference you need.
Why Ring Sizes Come in Letters and Numbers
Ring sizing systems evolved independently across different regions, leading to the variety of measurement methods we see today. The UK system uses alphabetic sizes from A to Z, reflecting a historical approach to standardization that prioritized sequential lettering. This system is used throughout the United Kingdom, Australia, New Zealand, Ireland, and South Africa.
The US system, by contrast, uses numeric sizes starting at 0.5 and going up to 16 (with some jewelers extending this range). The numbering system was designed to correspond roughly with finger circumference measurements, though the relationship is not perfectly linear.
The European system takes a more scientific approach, measuring ring sizes by inner circumference in millimeters. A European size 52, for example, indicates an inner circumference of 52mm. This system is used across most of continental Europe and provides a universal measurement standard that can be easily converted to any other system.
Despite these different systems, they all measure the same fundamental property: the inner diameter or circumference of the ring. Understanding these historical origins helps explain why different countries adopted different approaches to expressing the same measurement.
Letter to Number Ring Size Chart
Use this comprehensive chart to convert between UK letter sizes and US numeric sizes. The chart also includes EU measurements and inner diameter in millimeters for precise cross-referencing.
| UK Size | US Size | EU Size | Inner Diameter (mm) |
|---|---|---|---|
| A | 0.5 | 37 | 11.5 |
| B | 1 | 38 | 12.0 |
| C | 1.5 | 39 | 12.4 |
| D | 2 | 40 | 12.7 |
| E | 2.5 | 41 | 13.1 |
| F | 3 | 42 | 13.5 |
| G | 3.5 | 43 | 14.0 |
| H | 4 | 44 | 14.4 |
| I | 4.5 | 45 | 14.8 |
| J | 5 | 46 | 15.2 |
| J½ | 5.25 | 46.5 | 15.4 |
| K | 5.5 | 47 | 15.7 |
| K½ | 5.75 | 47.5 | 15.9 |
| L | 6 | 48 | 16.1 |
| L½ | 6.25 | 48.5 | 16.3 |
| M | 6.5 | 49 | 16.5 |
| N | 7 | 50 | 17.3 |
| O | 7.5 | 51 | 17.7 |
| P | 8 | 52 | 18.1 |
| Q | 8.5 | 53 | 18.5 |
| R | 9 | 54 | 19.0 |
| S | 9.5 | 55 | 19.4 |
| T | 10 | 56 | 19.8 |
| U | 10.5 | 57 | 20.2 |
| V | 11 | 58 | 20.6 |
| W | 11.5 | 59 | 21.0 |
| X | 12 | 60 | 21.4 |
| Y | 12.5 | 61 | 21.8 |
| Z | 13 | 62 | 22.2 |
Real-World Scenarios Where You Need This Chart
Understanding letter-to-number conversions is invaluable in many practical situations. Here are common scenarios where this guide becomes essential:
Vintage Ring Engraving
You inherited or found a vintage ring with "M" engraved inside the band. Using the chart above, you now know this corresponds to US size 6.5 with a diameter of 16.5mm. This knowledge helps you determine if it will fit or if resizing is needed.
International Shopping
An Australian friend tells you they wear size "P" and asks you to help find a ring from a US retailer. With this chart, you quickly convert P to US 8, making it easy to search for the correct size in American stores.
UK Online Shopping
A British Etsy seller lists a beautiful ring as "L½" but you're more familiar with US sizing. Referencing the chart, you immediately know this is equivalent to US 6.25 and has an inner diameter of 16.3mm, helping you visualize the fit.
Professional Jeweler Communication
Your jeweler gave you a ring in US size 7 but you're ordering a custom band from a UK artisan who works exclusively in letters. Now you know to request size "N" to ensure the band matches your existing ring perfectly.
Common Mistakes When Converting Letter to Number Sizes
Even experienced ring shoppers make these common errors when converting between letter and number sizes:
Mistaking Letters for Simple Numerals
Some people assume letter sizes follow a simple A=1, B=2, C=3 pattern that converts directly to numbers. This is incorrect. Letter "A" doesn't equal US size 1. UK "A" is actually US 0.5. Each letter position has a specific numeric correspondence that must be referenced on the chart.
Forgetting Half-Letter Sizes
The UK system includes many half-letter sizes like J½, K½, and L½, which represent important intermediate measurements. If you ignore these half-sizes, you could end up several millimeters off from the intended fit, resulting in a ring that's uncomfortable or won't stay on your finger.
Confusing US and EU Numeric Systems
The EU system also uses numbers (based on millimeter circumference), but EU 52 does not equal US 52. In fact, EU 52 corresponds to US 7. Confusing these systems can lead to ordering rings that are dramatically wrong sizes.
Not Using Diameter as Verification
The safest approach when dealing with unfamiliar sizing systems is to verify using the universal measurement: inner diameter in millimeters. If you rely only on letter-to-number conversion without double-checking the diameter measurement, you risk ordering an incorrect size.
The Diameter Cross-Check: Your Safety Net
While letter and number systems are useful for shopping and communication, the most reliable and universal way to verify ring size is through inner diameter measurement in millimeters. This measurement transcends all regional sizing systems and provides absolute certainty about whether a ring will fit.
How to Measure Your Ring Size by Diameter
To measure your ring's inner diameter, place your ring on a ruler with the ruler passing through the widest part of the inner circle. Read the measurement where the ruler crosses the inside edge on both sides, and note the distance between these two points. A millimeter ruler or caliper provides the most accuracy, though a standard ruler marked in millimeters works well.
When Your Measurement Falls Between Sizes
If your measurement falls between two sizes on the chart, consider these guidelines: If your measurement is exactly halfway between two sizes (for example, 16.4mm, which is halfway between M at 16.5mm and L½ at 16.3mm), you have flexibility. For new rings being ordered, you might round to the nearest half size. For vintage or heirloom rings, the actual measurement matters most for determining fit.
In general, if you're between sizes, round up slightly to ensure comfort and prevent the ring from rotating. A ring that's slightly loose can be easily resized by a jeweler, while a ring that's too tight is uncomfortable and potentially damaging to the band.
Using Technology for Verification
Modern technology offers additional verification methods. The Ring Sizer app uses your smartphone camera to measure ring diameter directly, providing millimeter precision by simply placing your ring on your phone screen and comparing it to reference measurements. This technology eliminates manual measurement errors and provides instant conversion to any sizing system.
Frequently Asked Questions
What is ring size 11 in letters?
Ring size 11 in the US system corresponds to UK size V, which has an inner diameter of 20.6mm. This is a popular size for men's rings and is also commonly worn by individuals with larger hands.
Are ring size letters the same worldwide?
No. The UK letter system (A through Z) is specifically used in the United Kingdom, Australia, New Zealand, Ireland, and South Africa. The US uses numeric sizes (0.5 to 16), and most of continental Europe uses millimeter circumference measurements. Several other countries have their own distinct sizing systems. Always verify which system is being used when shopping internationally.
What letter is a size 7 ring?
Ring size 7 in the US system is equivalent to UK size N, which has an inner diameter of 17.3mm. This is one of the most common women's ring sizes and represents the boundary between small and medium sizes.
Do men's rings use letters too?
Yes, men's rings use the exact same letter and number sizing systems as women's rings. However, men typically wear larger sizes, ranging from UK N to Z (equivalent to US 7 to 13), while women more commonly wear sizes from UK A to T (US 0.5 to 10). The difference is one of general body proportions rather than any separate system.
Get Precise Ring Sizing in Seconds
Stop guessing with letter and number conversions. The Ring Sizer app measures your ring's inner diameter directly on your phone screen, giving you accurate sizing across all systems.
Related Ring Sizing Resources
US to UK Ring Size Converter
Convert US numeric sizes to UK letter sizes with instant results.
EU to US Ring Size Converter
Convert European millimeter measurements to US numeric sizes.
US vs UK Ring Sizes
Comprehensive comparison of the two major ring sizing systems.
Complete Ring Size Chart
Master chart including all international sizing systems.
Ring Size Guide
Complete beginner's guide to finding your perfect ring size.
Ring Size Glossary
Definitions and explanations of ring sizing terminology.
Ring Sizing by Country
Different countries use different sizing systems. Learn how ring sizes work in specific regions: