Standard UK ring sizing reference
The UK, Ireland, and Australia use a letter-based scale that runs from A (smallest) through Z (largest), based on the same underlying measurement every system uses: the ring's inside circumference. Each letter is a fixed reference point on that scale, standardized across UK jewelers via British Standard BS 8721:2013.
For sizes larger than Z, jewelers typically extend the scale with Z+1, Z+2, and Z+3 rather than continuing the alphabet — those are less common but do come up for larger fingers or wide comfort-fit bands.
Each UK letter below is matched to its inside diameter, inside circumference, and closest US equivalent.
| UK Size | US Equivalent | Inside Diameter | Inside Circumference |
|---|---|---|---|
| UK F | US 3 | 14.1 mm | 44.2 mm |
| UK G | US 3.5 | 14.5 mm | 45.5 mm |
| UK H | US 4 | 14.9 mm | 46.8 mm |
| UK I | US 4.5 | 15.3 mm | 48.0 mm |
| UK J | US 5 | 15.7 mm | 49.3 mm |
| UK K | US 5.5 | 16.1 mm | 50.6 mm |
| UK L | US 6 | 16.5 mm | 51.9 mm |
| UK M | US 6.5 | 16.9 mm | 53.1 mm |
| UK N | US 7 | 17.3 mm | 54.4 mm |
| UK O | US 7.5 | 17.7 mm | 55.7 mm |
| UK P | US 8 | 18.1 mm | 57.0 mm |
| UK Q | US 8.5 | 18.5 mm | 58.3 mm |
| UK R | US 9 | 18.9 mm | 59.5 mm |
| UK S | US 9.5 | 19.3 mm | 60.8 mm |
| UK T | US 10 | 19.7 mm | 62.1 mm |
| UK U | US 10.5 | 20.1 mm | 63.4 mm |
| UK V | US 11 | 20.5 mm | 64.6 mm |
| UK W | US 11.5 | 20.9 mm | 65.9 mm |
| UK X | US 12 | 21.3 mm | 67.2 mm |
| UK Y | US 12.5 | 21.7 mm | 68.5 mm |
| UK Z | US 13 | 22.1 mm | 69.7 mm |
Need US, Japan, or EU sizing instead?
Open the converterFor every home method in one place, including common mistakes to avoid, see our complete measuring guide.
Ireland and Australia both use the same letter-based scale as the UK, so a UK N is also an Irish N and an Australian N — no conversion needed between those three. India commonly follows the same letter system as well, though it's always worth confirming with the specific jeweler, since some retailers there also use the US numeric scale.
Wider bands (roughly 6mm and up) tend to sit more snugly than a thin band at the same labeled size, so it's common to size up a quarter or half letter for a wide band — our guide to sizing for wide bands covers exactly how much. If you're between sizes, sizing up is usually the safer choice, since a slightly loose ring can be resized smaller more easily than a tight one can be resized larger.
Sizing a ring as a surprise? Our engagement ring sizing guide covers how to get a discreet, reliable estimate without asking directly.
There's no simple formula between the two — US uses numbers and UK uses letters, on completely different scales. The fastest way is to match your US size against the chart above, since both are cross-referenced against the same inside circumference. Our converter does this instantly if you'd rather skip the lookup, or see our full US Ring Size Chart.
EU and ISO sizing is usually given as the ring's inside circumference in millimeters rather than a letter, so a UK size like N works out to roughly 54mm (the same physical size as US 7). Use the circumference column in the chart above for the exact figure for any UK letter, or check our world comparison chart for every system side by side.
Wrap a strip of string or paper snugly around the base of your finger, mark where it overlaps, then measure that length against a ruler in millimeters — match it to the circumference column above. Our full measuring guide covers this and two other methods in detail.
UK ring sizes are a letter-based scale from A to Z, standardized under British Standard BS 8721:2013, where each letter represents a specific inside circumference in millimeters. It's the same underlying measurement the US, Japan, and EU systems use — just labeled differently.
UK size W is equivalent to US 11.5, with an inside circumference of about 65.9mm. You can find any other UK letter's US, Japan, and EU equivalent in the chart above, or convert it automatically with our converter.
Yes — Ireland and Australia both use the identical letter-based scale as the UK, so a UK N is also an Irish N and an Australian N with no conversion needed. India commonly follows the same system too, though it's worth confirming with the specific jeweler.
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© Rings Sizer. Sizes are estimates — confirm in person for a permanent purchase.