What is a US size 7 in UK sizes?
A UK N½. Both correspond to an inside circumference of about 54.4 mm and an inside diameter of 17.3 mm. Some charts round this to UK N; the millimetre figure is the same either way.
US ring size to UK conversion
US numbers and UK letters are unrelated scales with no formula between them. Here is the lookup, and the reason the two never quite line up.
Ring size calculator
Enter a measurement to get your US size, then read across the chart for the UK letter.
Your size
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Enter a measurement in millimetres
Part of a larger guide
This page covers one conversion corridor in depth: US numbers to UK letters. For a complete overview, see the international ring size conversion guide.
The two systems are unrelated. The US uses numbers, the UK uses letters, and there is no formula connecting them — a US 7 is not a UK G because it is the seventh letter. You need a lookup, which is what this page is.
The UK letter system is used across the UK, Ireland, Australia and New Zealand, and is sometimes called the Wheat Sheaf scale. South Africa uses it too. If a retailer quotes you a letter, this is the scale they mean.
The conversion chart
| US / Canada | UK / AU / IE | Inside circumference | Inside diameter |
|---|---|---|---|
| 3 | F | 44.2 mm | 14.1 mm |
| 3.5 | G | 45.5 mm | 14.5 mm |
| 4 | H | 46.8 mm | 14.9 mm |
| 4.5 | I | 48.0 mm | 15.3 mm |
| 5 | J½ | 49.3 mm | 15.7 mm |
| 5.5 | K½ | 50.6 mm | 16.1 mm |
| 6 | L½ | 51.9 mm | 16.5 mm |
| 6.5 | M½ | 53.1 mm | 16.9 mm |
| 7 | N½ | 54.4 mm | 17.3 mm |
| 7.5 | O½ | 55.7 mm | 17.7 mm |
| 8 | P½ | 57.0 mm | 18.1 mm |
| 8.5 | Q½ | 58.2 mm | 18.5 mm |
| 9 | R½ | 59.5 mm | 18.9 mm |
| 9.5 | S½ | 60.8 mm | 19.4 mm |
| 10 | T½ | 62.1 mm | 19.8 mm |
| 10.5 | U½ | 63.4 mm | 20.2 mm |
| 11 | V½ | 64.6 mm | 20.6 mm |
| 11.5 | W½ | 65.9 mm | 21.0 mm |
| 12 | X½ | 67.2 mm | 21.4 mm |
| 12.5 | Y½ | 68.5 mm | 21.8 mm |
| 13 | Z½ | 69.7 mm | 22.2 mm |
Why US whole sizes land on UK half-letters
Look at the chart and you will notice something odd: from US 5 upward, every whole US size maps to a UK half-letter. US 6 is L½, US 7 is N½, US 8 is P½. That is not a rounding fudge, and it is worth understanding because it explains why conversions between the two systems always feel slightly off.
The reason is that the two scales have different step sizes and different starting points. A full US size is about 2.5 mm of circumference. A single UK letter step is about 1.25 mm — half as much. So one US size covers roughly two UK letters, and because the scales do not begin at the same place, the US whole numbers happen to land between UK letters rather than on them.
The rule of thumb
One US size ≈ two UK letters. So US 6 → L½, US 7 → N½, US 8 → P½, US 9 → R½, US 10 → T½. Counting up two letters per US size from any anchor point gets you close.
The UK letter scale itself
Each UK letter corresponds to a specific inside circumference. This is the underlying scale the conversion is derived from, so you can check any row of the chart above against it yourself.
| UK letter | Inside circumference | Inside diameter |
|---|---|---|
| A | 37.8 mm | 12.0 mm |
| B | 39.1 mm | 12.4 mm |
| C | 40.4 mm | 12.9 mm |
| D | 41.7 mm | 13.3 mm |
| E | 42.9 mm | 13.7 mm |
| F | 44.2 mm | 14.1 mm |
| G | 45.5 mm | 14.5 mm |
| H | 46.8 mm | 14.9 mm |
| I | 48.0 mm | 15.3 mm |
| J | 48.7 mm | 15.5 mm |
| K | 50.0 mm | 15.9 mm |
| L | 51.2 mm | 16.3 mm |
| M | 52.5 mm | 16.7 mm |
| N | 53.8 mm | 17.1 mm |
| O | 55.1 mm | 17.5 mm |
| P | 56.3 mm | 17.9 mm |
| Q | 57.6 mm | 18.3 mm |
| R | 58.9 mm | 18.7 mm |
| S | 60.2 mm | 19.2 mm |
| T | 61.4 mm | 19.5 mm |
| U | 62.7 mm | 20.0 mm |
| V | 64.0 mm | 20.4 mm |
| W | 65.3 mm | 20.8 mm |
| X | 66.6 mm | 21.2 mm |
| Y | 67.8 mm | 21.6 mm |
| Z | 69.1 mm | 22.0 mm |
One quirk worth noting: the step from I to J is smaller than the others — 48.0 mm to 48.7 mm, against roughly 1.25 mm elsewhere. That irregularity is genuinely in the historical scale, not an error here, and it is why US 4.5 lands exactly on I while US 5 lands on J½.
Converting a UK letter to a US size
Read the chart in reverse, or work from the circumference. Because both systems are ultimately labels for a millimetre measurement, going through the millimetres is always reliable:
- Find your UK letter's circumference From the letter scale above. A UK N is 53.8 mm.
- Find the nearest US size at that circumference 53.8 mm sits between US 6.5 (53.1 mm) and US 7 (54.4 mm), slightly closer to US 7.
- If it falls between, take the larger A ring half a letter too large is wearable and easily sized down. One too small is not wearable at all.
Sizes above Z
The UK scale runs A to Z and then continues as Z½, Z+1, Z+2 and so on. Larger US sizes fall into this range: US 13 corresponds to roughly Z½. Notation above Z varies between jewellers, so if you are ordering at that end of the scale, quote the circumference in millimetres rather than the letter.
Ordering across the two systems
Never assume a bare number is your system
If a listing says "size 7" without saying which system, ask. UK retailers occasionally list numeric sizes for international customers, and a UK site quoting a number may or may not mean the US scale. When in doubt, give the retailer your inside circumference in millimetres — that figure is unambiguous everywhere.
It is also worth remembering that published charts differ slightly between manufacturers, and the US-to-UK correspondence in particular is one where you will see small disagreements between sources. Some charts list US 7 as UK N rather than N½. Both are defensible; the underlying circumference is 54.4 mm either way, and that is the figure to quote if precision matters.
How reliable are these conversions?
The millimetre figures are consistent and checked, but the size labels attached to them are convention rather than enforced standard. Published charts vary between manufacturers by up to roughly a quarter of a size. When precision matters, quote the inside circumference in millimetres and use the retailer's own chart rather than a general one.
US and UK conversion questions
What is a UK size N in US sizes?
A UK N is 53.8 mm of circumference, which sits between US 6.5 (53.1 mm) and US 7 (54.4 mm), slightly nearer US 7. If you are ordering and cannot try it on, US 7 is the safer of the two.
How many UK letters is one US size?
About two. A full US size is roughly 2.5 mm of circumference and a UK letter step is roughly 1.25 mm, so counting two letters per US size from a known anchor gets you close. US 6 is L½, US 7 is N½, US 8 is P½.
Do Australia and Ireland use the UK letter system?
Yes. Australia, New Zealand, Ireland and South Africa all use the same letter scale as the UK, so a UK conversion works for all of them. Canada follows the US numeric system rather than the UK one.
What comes after Z in UK ring sizes?
The scale continues as Z½, then Z+1, Z+2 and so on. US 13 is roughly Z½. Notation above Z is not fully consistent between jewellers, so at that end of the scale it is safer to quote your inside circumference in millimetres.
Where to go next
US to EU sizes
A completely different logic — the EU size is the measurement itself.
All the sizing systemsJapan, Switzerland, India and the rest, and how each one is built.
The full millimetre chartEvery system side by side with both physical measurements.
Get your circumferenceThe unambiguous figure to quote when ordering internationally.