Ring Size Conversion Chart: US, UK, EU, mm, cm & Inches
The quick answer
A ring size is really just a circumference measurement wearing a different label depending on which country’s chart you’re reading. If you already have a measurement in mm, cm, or inches, skip straight to the table below and match it to the closest US column — that’s your size, full stop. If you’re converting a UK, EU, or India size to US instead, use the second table; there’s no universal formula between letter-based and number-based systems, so a lookup table is the only reliable method.
- Have a measurement in mm or cm? Match it in the “Circumference” column below.
- Have a UK letter size (like “M” or “P½”)? Jump to the international conversion table.
- Don’t have a measurement yet? Get one first with our how to measure ring size guide, or use the ring size calculator directly.
Full ring size conversion chart (US to mm, cm, inches)
This is the table to bookmark — every US half-size from 3 to 13, cross-referenced against the three measurement units people actually search for.
| US Size | Diameter (mm) | Circumference (mm) | Circumference (cm) | Circumference (in) |
|---|---|---|---|---|
| 3 | 14.1 | 44.2 | 4.42 | 1.74 |
| 3.5 | 14.5 | 45.5 | 4.55 | 1.79 |
| 4 | 14.9 | 46.8 | 4.68 | 1.84 |
| 4.5 | 15.3 | 48.0 | 4.80 | 1.89 |
| 5 | 15.7 | 49.3 | 4.93 | 1.94 |
| 5.5 | 16.1 | 50.6 | 5.06 | 1.99 |
| 6 | 16.5 | 51.9 | 5.19 | 2.04 |
| 6.5 | 16.9 | 53.1 | 5.31 | 2.09 |
| 7 | 17.3 | 54.4 | 5.44 | 2.14 |
| 7.5 | 17.7 | 55.7 | 5.57 | 2.19 |
| 8 | 18.1 | 57.0 | 5.70 | 2.24 |
| 8.5 | 18.5 | 58.3 | 5.83 | 2.30 |
| 9 | 18.9 | 59.5 | 5.95 | 2.34 |
| 9.5 | 19.3 | 60.8 | 6.08 | 2.39 |
| 10 | 19.8 | 62.1 | 6.21 | 2.44 |
| 10.5 | 20.2 | 63.4 | 6.34 | 2.50 |
| 11 | 20.6 | 64.6 | 6.46 | 2.54 |
| 11.5 | 21.0 | 65.9 | 6.59 | 2.59 |
| 12 | 21.4 | 67.2 | 6.72 | 2.65 |
| 12.5 | 21.8 | 68.5 | 6.85 | 2.70 |
| 13 | 22.2 | 69.7 | 6.97 | 2.74 |
Which column should you actually use? Circumference, not diameter, almost always — it’s what a string, paper strip, or soft tape measure gives you when wrapped around the finger. Diameter matters when you’re measuring a rigid object like an existing ring, since you can lay a ruler straight across it but can’t easily wrap a tape around it accurately.
Converting a cm or mm measurement directly
If you measured in centimeters — a common result from wrapping string around your finger and reading a metric ruler — the values you’re searching for are almost always circumference, not diameter. A 6cm ring size lands close to a US 9.5 (60.8mm), and a 7cm ring size lands close to a US 13 (69.7mm). If your number falls between two rows, round to the nearest, and round up rather than down when you’re unsure, per the sizing guidance in our measuring guide.
Millimeter measurements work the same way — just use the mm column directly. A common trouble spot is a measurement like “16.5mm to inches”: that’s 0.65 inches, but for ring sizing, a 16.5mm figure is almost never a circumference (66mm circumference range corresponds to a much larger ring); it’s more likely a diameter reading taken from an existing ring, which corresponds to roughly a US size 6.5 on the Diameter column above. If a number you’ve measured doesn’t seem to land anywhere sensible on this chart, double check whether you actually measured diameter or circumference — it’s the single most common mix-up in ring sizing, and the two numbers for the same ring differ by roughly 3.14x (circumference = diameter × π).
Converting inches to ring size
Inch measurements usually show up as fractions from an old-fashioned tailor’s tape or a printed ring sizer marked in imperial units. Convert the fraction to a decimal first, then match it against the inches column in the table above — for example, 2⅝ inches is 2.625in, which sits closest to a US size 11.5 to 12. A measurement of 2¾ inches (2.75in) rounds to the top of the chart at a US size 13.
If your fraction doesn’t convert cleanly, this quick reference covers the most commonly searched values:
| Fraction | Decimal (in) | Closest US size |
|---|---|---|
| 2 1/8″ | 2.125 | 6 |
| 2 1/4″ | 2.25 | 7.5 |
| 2 3/8″ | 2.375 | 9 |
| 2 1/2″ | 2.50 | 10.5 |
| 2 5/8″ | 2.625 | 11.5–12 |
| 2 3/4″ | 2.75 | 13 |
US to UK, Europe & India ring size conversion
Unlike metric conversions, there’s no formula between the US numeric system and the UK’s letter-based system (or the similar systems used across Europe and India) — the scales were built independently, so a lookup table is the only reliable path. Treat the figures below as close approximations; brands occasionally round differently, so for a specific retailer’s ring, check their own size chart if one is available before ordering internationally.
| US Size | UK/Ireland/Australia | EU | India (approx.) |
|---|---|---|---|
| 3 | F | 44 | 4 |
| 4 | H | 46.5 | 8 |
| 5 | J½ | 49 | 10 |
| 6 | L½ | 51.5 | 12 |
| 7 | N½ | 54 | 15 |
| 8 | P½ | 56.5 | 17 |
| 9 | R½ | 59 | 19 |
| 10 | T½ | 61.5 | 21 |
| 11 | V½ | 64 | 24 |
| 12 | X½ | 66.5 | 26 |
| 13 | Z½ | 68.5 | 28 |
India’s system in particular varies more between individual jewelers than the US, UK, or EU charts do — if you’re ordering from a specific Indian retailer, treat this column as a starting estimate and confirm against their own printed chart when possible.
All Ring Sizing Charts
Find the perfect ring size guide for every brand, style, and occasion. Click any chart below to view the full sizing reference.
Frequently asked questions
Is a UK ring size the same as a US ring size?
No — they're different scales entirely. A US size 7 is roughly a UK N½, not a UK "7." Always convert through a lookup table rather than assuming the numbers translate directly; several UK retailers do also stock rings in a "7" labeled size, but that's a coincidence of two different systems, not equivalence.
How do I convert my ring size from cm to inches or mm?
Multiply centimeters by 10 to get millimeters, or divide by 2.54 to get inches. But the more useful step is usually skipping the unit math entirely and matching your raw cm or mm figure straight to the corresponding row in the main chart above, which already has the size for you.
What does "ring size conversion chart" actually need to show, that a basic size chart doesn't?
A true conversion chart cross-references multiple measurement systems side by side — US numbers, UK/EU/India equivalents, and the raw physical millimeter and inch measurements — so you can arrive at a size no matter which unit your starting measurement happens to be in. A basic size chart usually only lists one system.
My measurement doesn't match any row exactly — what do I do?
Round to the nearest listed size, and when you're between two, round up rather than down; a ring that's a touch loose is a cheap resize, while one that won't pass the knuckle often means a return. For the full reasoning on this, see the "what if I'm between sizes" section of our measuring guide.
Do men's and women's rings use different conversion charts?
No — the conversion tables above apply identically regardless of gender; a US size 9 converts to the same UK, EU, and India equivalents either way. What differs between genders is which sizes are ordered most often, which we cover in our ring size guide by finger and gender.