Standard US ring sizing reference, in millimeters
The United States and Canada use a numeric scale that runs in half-size steps, typically from about size 3 up to size 13 for adults, though some jewelers stock quarter sizes for a finer fit. Each number corresponds to a specific inside circumference of the ring, measured in millimeters — the higher the number, the larger the ring's inner opening.
Unlike the UK's letter-based system or Japan's own numeric scale, the US system doesn't map directly onto a simple formula you can do in your head. It's a fixed reference table, standardized across US jewelers, which is exactly why a printed or digital chart is the fastest way to find your size — or to convert it into another country's system if you're ordering internationally.
This chart shows the inside diameter and inside circumference behind each US size, in millimeters. If you already have a ring that fits, measuring its inside diameter against this table is one of the most reliable ways to confirm your size at home.
Quick reference: US 6 ≈ 51.9mm circumference, US 7 ≈ 54.4mm, US 8 ≈ 57.0mm, US 9 ≈ 59.5mm, US 13 ≈ 69.7mm — the full table below covers every US size from 3 to 13 in mm.
| US Size | Inside Diameter | Inside Circumference |
|---|---|---|
| US 3 | 14.1 mm | 44.2 mm |
| US 3.5 | 14.5 mm | 45.5 mm |
| US 4 | 14.9 mm | 46.8 mm |
| US 4.5 | 15.3 mm | 48.0 mm |
| US 5 | 15.7 mm | 49.3 mm |
| US 5.5 | 16.1 mm | 50.6 mm |
| US 6 | 16.5 mm | 51.9 mm |
| US 6.5 | 16.9 mm | 53.1 mm |
| US 7 | 17.3 mm | 54.4 mm |
| US 7.5 | 17.7 mm | 55.7 mm |
| US 8 | 18.1 mm | 57.0 mm |
| US 8.5 | 18.5 mm | 58.3 mm |
| US 9 | 18.9 mm | 59.5 mm |
| US 9.5 | 19.3 mm | 60.8 mm |
| US 10 | 19.7 mm | 62.1 mm |
| US 10.5 | 20.1 mm | 63.4 mm |
| US 11 | 20.5 mm | 64.6 mm |
| US 11.5 | 20.9 mm | 65.9 mm |
| US 12 | 21.3 mm | 67.2 mm |
| US 12.5 | 21.7 mm | 68.5 mm |
| US 13 | 22.1 mm | 69.7 mm |
Want this converted to UK, Japan, or EU sizing automatically?
Open the converterQuick answer: The average US ring size for women is about size 6, with most falling somewhere between 5 and 7. The average for men is about size 9 to 10, with most falling between 8 and 11.
These are population averages, not predictions for any individual finger — actual size varies a lot from person to person regardless of height, weight, or gender. If you're sizing for yourself, an average is a poor substitute for an actual measurement; use it only as a rough starting point if you have absolutely nothing else to go on, such as when estimating a partner's size secretly for a proposal.
Height and weight are sometimes suggested as a way to estimate ring size, but the correlation is weak in practice — plenty of tall, heavier people have slim fingers, and plenty of petite people don't. If you're working from an estimate rather than a real measurement, treat the result as a wide range (often a full size or more of uncertainty) rather than a single confident number, and size up slightly if you have to guess, since a loose ring is far easier to fix than a tight one.
For a full walkthrough of every home method, including measuring an existing ring, see our complete measuring guide. Prefer something you can cut out and wrap around your finger instead of a ruler? Try our Printable Ring Sizer for Women's Sizes, which works for men's sizing too.
Most US jewelers stock half sizes as standard, and many offer quarter sizes for rings that need a very precise fit. If your measurement falls between two sizes on the chart, sizing up rather than down is usually the safer choice — a slightly loose ring can be resized smaller far more easily than a tight one can be resized larger.
Band width also affects fit at a given labeled size: wider bands (roughly 6mm and up) tend to sit more snugly than a thin band of the same size, so it's common to size up by a quarter or half size for a wide band, or to choose a comfort-fit inner edge, which makes any width easier to get on and off. If you're sizing a ring as a surprise, our engagement ring sizing guide covers how to get it right without asking.
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 and match it to the circumference column above. Our full measuring guide covers this and two other methods, and our existing-ring tool works if you already own a ring that fits.
The average US ring size for women is about size 6, though most women fall somewhere between 5 and 7. That's a population average, not a prediction for any individual finger — always measure directly rather than assuming an average applies to you.
Ring sizes are measured in millimeters, not centimeters, so multiply your cm measurement by 10 first. A 7cm circumference, for example, is 70mm, which lines up closest to a US size 13 on the chart above.
Every US ring size corresponds to a specific inside diameter and inside circumference in millimeters — for example, US 6 is 16.5mm diameter (51.9mm circumference) and US 9 is 18.9mm diameter (59.5mm circumference). The full mm breakdown for sizes 3 through 13 is in the chart above.
European sizes are usually just the ring's inside circumference in millimeters, so a EU 54 is close to a US 7 and a EU 52 is close to a US 6. Rounding conventions vary slightly by country, so use the exact circumference in the chart above or our converter for a precise match rather than a fixed formula.
UK letters and US numbers both describe the same inside circumference, just labeled differently — UK J is close to US 5, UK P is close to US 8, and UK R is close to US 9. See our full UK Ring Size Chart for the complete letter-by-letter breakdown.
Yes — Canada uses the identical numeric scale as the US, so no conversion is needed between the two. The UK, Mexico, and most of continental Europe use different scales, so those do require converting; see our world comparison chart for every system side by side.
A US 5 has an inside diameter of about 15.7mm, a US 7 is about 17.3mm, and a US 10 is about 19.7mm — each step up the scale adds roughly 0.4mm of diameter, or about 1.3mm of circumference.
Free ring size conversion and measurement tools for US, UK, Japan, and international sizing systems.
© Rings Sizer. Sizes are estimates — confirm in person for a permanent purchase.