US Ring Sizes vs UK Ring Sizes

5 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

US ring sizes use numbers (1–15); UK ring sizes use letters (A–Z with half steps). They are completely different systems with no simple offset that converts one to the other. Both ultimately describe the same physical ring — the inner diameter in millimeters — but express it in entirely different terms.

When buying from a British jeweler (including many online jewelry brands) or receiving a ring as a gift from the UK, knowing the conversion is essential. An engagement ring purchased in the UK or US as a surprise must be in the right size system for the receiving jeweler to understand the fit.

US to UK Conversion Table

US    UK    Diam (mm)
──    ──    ─────────
 4    H½    15.0
 4.5  I½    15.3
 5    J½    15.7
 5.5  K½    16.1
 6    L½    16.5
 6.5  M½    16.9
 7    N½    17.3
 7.5  O½    17.7
 8    P½    18.2
 8.5  Q½    18.6
 9    R½    18.9
 9.5  S½    19.4
10    T½    19.8

How the UK System Works

UK ring sizes use letters A through Z, with half sizes (A½, B½, etc.) in between. Each letter step corresponds to approximately 0.4 mm change in inner diameter. The alphabet runs from size A (diameter ~11.9 mm, very small) to Z+6 for very large fingers.

The half-size notation (N½, P½) is standard in UK jewelry. A UK N½ is a common women's size; UK T½ is a typical men's size. The UK system is also used in Ireland, Australia, New Zealand, and South Africa.

Using Diameter as the Common Language

When a UK jeweler and a US customer need to communicate ring size, inner diameter in millimeters is the universal reference point. A ring with an inner diameter of 17.35 mm is a US 7 and a UK N½. Share the diameter measurement with any jeweler worldwide and they can work from it.

If you have a ring that fits and want to find both sizes: measure the inner diameter with a ruler in millimeters, then use the table above to find both US and UK sizes.

Quick Tips

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US 7 = UK N½ — this is the most common women's ring size and a useful anchor.
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US 10 = UK T½ — a common men's ring size.
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When ordering from a UK jeweler, specify the diameter in mm if you are unsure of the UK letter.
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UK, Australian, New Zealand, and South African jewelers all use the same letter-based system.

Frequently Asked Questions

What is US ring size 6 in UK?

US 6 ≈ UK L½. Inner diameter approximately 16.5 mm.

What is UK ring size N in US?

UK N ≈ US 6.75. The nearest standard US sizes are 6.5 or 7.

Does Australia use UK ring sizes?

Yes. Australia, New Zealand, and South Africa all use the same letter-based ring sizing system as the UK.

Is the UK ring size system used anywhere else?

The UK system (letter-based) is standard in the UK, Ireland, Australia, New Zealand, and South Africa. Continental Europe uses the EU system (mm circumference). The US uses its own numeric scale.

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