US to UK Ring Size Converter: Full Chart with Half Sizes
Last updated: February 2026
Ring sizing can be confusing when shopping internationally or receiving gifts from friends abroad. The United States and United Kingdom use completely different ring sizing systems, which means a size 7 ring in the US is not the same as a size 7 in the UK—in fact, the UK doesn't use numeric sizes at all. Understanding how to convert between these systems is essential when purchasing rings from British jewelers, Australian brands, or any retailer operating under the UK measurement standard.
Whether you're buying an engagement ring from Hatton Garden in London, ordering from a British brand online, or receiving a vintage ring from the UK, knowing your ring size in both systems ensures perfect fit and eliminates costly returns. This comprehensive guide walks you through both sizing systems, provides a complete conversion chart with exact measurements, and shares insider tips to avoid common conversion mistakes.
The good news: once you understand the relationship between US and UK sizes, converting takes seconds. We'll also show you how to verify your converted size using measurements so you can shop with confidence internationally.
How the US and UK Sizing Systems Work
Both US and UK ring sizes are based on the inner diameter and circumference of the ring, but they express these measurements using completely different scales. Understanding this fundamental difference is key to accurate conversion.
US Ring Sizing System
The United States uses a numeric sizing system ranging from size 3 to size 16, based on the inner circumference of the ring measured in millimeters. The US system allows for half and even quarter sizes (like 7.25 or 8.75), providing precision for different hand proportions. Each full size increment represents a circumference increase of approximately 1.5 millimeters. The system was historically based on the diameters of ring mandrels used by American jewelers, and it remains the standard for all major US retailers and independent jewelers today.
UK Ring Sizing System
The United Kingdom uses an alphabetic sizing system that progresses from A to Z, and then continues with sizes like Z+1 for larger rings. Instead of numeric increments, the UK system uses letters, with each letter representing a specific circumference range. The UK system also includes half-letter sizes (indicated by ½ or using ½ designations), providing similar flexibility to the US system but with a different visual representation. This system is standard throughout the UK, Australia, New Zealand, and parts of Europe.
US to UK Ring Size Conversion Chart
This chart provides the complete conversion from US numeric sizes to UK letter sizes across the full range of common ring sizes. Each row includes the inner diameter in millimeters and the circumference in millimeters for reference, allowing you to verify your size using direct measurement as well.
| US Size | UK Size | Inner Diameter (mm) | Circumference (mm) |
|---|---|---|---|
| 3 | F | 14.6 | 45.8 |
| 3.5 | G | 15.1 | 47.3 |
| 4 | H | 15.6 | 49.0 |
| 4.5 | I | 16.1 | 50.6 |
| 5 | J½ | 16.5 | 51.8 |
| 5.5 | K½ | 17.0 | 53.4 |
| 6 | L½ | 17.5 | 54.9 |
| 6.5 | M½ | 18.0 | 56.5 |
| 7 | N½ | 17.3 | 54.4 |
| 7.5 | O½ | 18.5 | 58.1 |
| 8 | P½ | 19.0 | 59.7 |
| 8.5 | Q½ | 19.5 | 61.2 |
| 9 | R½ | 19.9 | 62.5 |
| 9.5 | S½ | 20.4 | 64.1 |
| 10 | T½ | 20.9 | 65.6 |
| 10.5 | U½ | 21.3 | 66.9 |
| 11 | V½ | 21.8 | 68.5 |
| 11.5 | W½ | 22.3 | 70.0 |
| 12 | X½ | 22.8 | 71.6 |
| 12.5 | Z | 23.2 | 72.9 |
| 13 | Z+1 | 23.7 | 74.5 |
Use this chart as your reference when ordering from UK retailers, Australian jewelers, or any shop using alphabetic sizing. If your US size falls between listed sizes, round to the nearest half size for optimal fit.
Common Conversion Mistakes and How to Avoid Them
Even experienced online shoppers make errors when converting between ring sizing systems. Here are the three most common mistakes and practical strategies to prevent them.
Mistake 1: Assuming UK Sizes Map 1:1 to US Numbers
The most common error is thinking a UK size 7 equals a US size 7. This is incorrect. The UK system uses letters (A through Z+), while the US system uses numbers (3 through 16). There is no direct numeric correlation. A US size 7 converts to UK size N½, not UK size 7. Always use a conversion chart or calculator rather than guessing based on number matching.
Solution: Reference the chart above every time you shop internationally, or save this page for quick access.
Mistake 2: Ignoring Half Sizes in the UK System
Some shoppers assume the UK system only uses whole letter sizes (A, B, C, etc.) without half-size options. This is false. The UK system extensively uses half-letter sizes (A½, B½, etc.), and these are as important for proper fit as full sizes. If you don't specify a half size when needed, you may receive a ring that's either too loose or uncomfortable. The conversion chart above explicitly includes these half sizes to ensure you order the correct designation.
Solution: When converting your US size, always include the half-size designation if it appears in the conversion chart. Double-check with the retailer if unsure about their notation.
Mistake 3: Not Accounting for Band Width
Ring size is primarily based on inner diameter, but band width significantly affects how a ring feels on the finger. A wide band (6mm or more) will sit tighter on the same finger circumference than a narrow band (2-3mm). Many international shoppers don't realize their size might change by half a size when moving from a narrow band to a wide band or vice versa. If you're used to wearing a delicate band and ordering a chunky statement ring, you may need to go up a half size.
Solution: For wide bands, consider sizing up by half a size for comfort. Always check the band width specifications when ordering and compare with rings you currently own.
How to Verify Your Converted Size
Rather than relying solely on conversion charts, you can independently verify your ring size using actual measurements. This approach eliminates guesswork and increases confidence when ordering from international retailers.
Cross-Check with Inner Diameter in Millimeters
The most reliable method is measuring the inner diameter of a ring that fits perfectly. All ring sizes, whether US or UK, correspond to specific inner diameter measurements. If you know your inner diameter in millimeters, you can match it to the conversion chart above without any ambiguity. Jewelers consider a ring fit when the inner diameter matches within 0.2-0.3mm, which is the tolerance for comfort and safety.
For example, if you measure a ring that fits perfectly and find the inner diameter is 17.3mm, you can see from the chart that this corresponds to US size 7 and UK size N½. This measurement-based approach works regardless of regional sizing systems.
Measure an Existing Ring's Inner Diameter
Take a ring from your collection that fits comfortably on the finger where you want to wear the new ring. Measure the inner diameter using a ruler or calipers. Place the ruler across the inside opening of the ring and measure from the inner edge on one side to the inner edge on the opposite side. Record this measurement in millimeters.
If you don't have calipers or a precise ruler, many jewelers offer free sizing services and will measure an existing ring for you. A quick visit to a local jewelry shop takes five minutes and provides definitive measurements you can use for any online purchase worldwide.
Use the Ring Sizer App for On-Screen Verification
The Ring Sizer app provides an additional verification method by allowing you to measure your finger on-screen and receive both US and UK size recommendations simultaneously. This tool cross-references measurements against the same standardized charts jewelers use, giving you confidence that your conversion is accurate. Using the app alongside this chart ensures you're making informed decisions before purchasing rings internationally.
The app also stores your size information, making future conversions instant when you're browsing different international retailers.
When You'll Need This Conversion
Ring size conversion is relevant in specific purchasing scenarios. Knowing when to use this chart helps you avoid expensive ordering mistakes.
Buying from UK Jewelers Online
London's Hatton Garden district houses some of the world's finest independent jewelers, many of whom sell online globally. Luxury British brands like Annoushka, Astrid & Miyu, and Tiffany UK locations use the UK alphabetic system. When ordering a custom engagement ring, antique piece, or fine jewelry from these retailers, conversion is essential for getting the right fit on your first order.
Ordering from Australian and New Zealand Shops
Australia and New Zealand adopted the UK ring sizing system, so all major Australian jewelers and retailers use UK letter sizes. If you're ordering from Australian brands (which have become increasingly popular for ethical sourcing and unique designs), use this conversion chart to ensure your size aligns with their specifications.
Gifting Rings Internationally
If you're surprising someone with a ring purchased from a UK or Australian retailer, conversion ensures the gift arrives in the correct size. International ring gifting is risky if the recipient doesn't know your conversion, so share both their US and UK sizes with the jeweler to minimize resizing costs.
Resizing a Ring Bought Abroad
When you have a vintage ring from the UK or inherit jewelry with a UK size marking, converting to US helps you communicate with American jewelers during resizing. Understanding that your UK size M equals US size 6.5, for instance, speeds up the resizing process and ensures the jeweler adjusts to the correct fit.
Frequently Asked Questions
Is UK ring size the same as Australian ring size?
Yes, Australian and UK ring sizes are identical. Both countries use the same alphabetic system (A through Z+) based on the same circumference standards. When shopping from Australian jewelers online, use this conversion chart directly without modification. New Zealand also uses the UK system. This simplifies international shopping across these countries—one conversion covers all three regions.
What is a US size 7 in UK?
A US size 7 converts to UK size N½. This corresponds to an inner diameter of 17.3 millimeters and a circumference of 54.4 millimeters. This is one of the most common ring sizes globally, so if this is your size, you'll find inventory in both US and UK retailers, though the selection differs by brand and style availability.
Do UK ring sizes have half sizes?
Yes, the UK system extensively uses half-letter sizes, indicated by a ½ symbol after the letter (such as A½, B½, M½, etc.). Half sizes in the UK system provide the same level of precision as half sizes in the US numeric system. This means if you're between two full sizes, the UK jeweler will have a half-size option available, preventing the need for custom sizing or uncomfortable fits.
Can I order a ring in UK size and have it shipped to the US?
Yes, many UK and international jewelers ship to US addresses. International shipping costs vary but are often reasonable for small items like rings. Ensure the jeweler can ship to your state (some jewelry retailers have restrictions) and confirm shipping times before ordering, as resizing after international delivery can add delays. Always verify return policies before purchase, as international returns can be costly and time-consuming if the size doesn't fit perfectly.
What if my ring size is between two UK sizes?
If you measure your inner diameter and it falls between two sizes, contact the jeweler before ordering. Most jewelers can create a custom ring in a size between standard options. Alternatively, round to the larger size for comfort and have the ring resized down slightly if needed. It's easier to resize a ring down by a small amount than to size it up significantly.
Related Ring Size Conversions & Tools
Need to convert to other sizing systems? Explore these related tools and comparisons to understand ring sizing across different countries and regions.
EU to US Ring Size Converter
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Letter to Number Ring Size Converter
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US vs UK Ring Sizes Comparison
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Complete Ring Size Chart
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Country-Specific Ring Sizing Guides
Learn about ring sizing standards in specific countries and regions to understand how sizes are determined and used globally.
Deep Dive Into Ring Sizing
Want comprehensive information about ring sizing beyond conversion? Read our detailed guides and articles about how ring sizes work, history of sizing systems, and tips for getting the perfect fit.
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