Ring Size Converter
Enter your finger measurement as an inside diameter or inside circumference, in millimetres or inches, and this converter shows your equivalent ring size across six international standards: US/Canada, UK/Australia, EU/France/Russia, Germany, Switzerland, and Japan/China. Results update instantly, and a full reference chart below lets you scan all sizes at a glance.
How ring sizes work around the world
There is no single global ring-size standard, which makes buying jewelry abroad or online genuinely confusing. The US and Canada use a decimal number scale, typically running from size 3 to 15 in half-step increments. The UK, Australia, South Africa, and New Zealand use an alphabetic system from F to Z+6. Continental Europe (France, Russia, Belgium, Scandinavia) defines the EU size simply as the inner circumference of the ring in millimetres, so EU 54 means a 54 mm circumference. Germany defines its size as the inner diameter in millimetres, making conversion from any measurement very direct. Switzerland uses the EU figure minus 40. Japan and China share a separate numeric scale that does not directly correspond to diameters in whole millimetres but follows a consistent mapping.
How to measure your ring size at home
The most reliable method is to measure the inner diameter of a ring that already fits well. Lay the ring on a ruler and read the distance between the two inner edges of the band in millimetres, then look it up in the table. If you do not have a ring to measure, cut a thin strip of paper or use a piece of string, wrap it snugly around the base of the finger you want to measure (not over the knuckle), mark where the ends meet, lay it flat, and measure its length with a ruler. That length is your inner circumference in millimetres. Use the "Inside circumference" mode to convert it directly. For the most accurate result, measure at the end of the day when fingers are slightly larger, avoid measuring in very cold conditions, and measure the specific hand and finger the ring will be worn on, since the same finger on different hands can differ by half a size.
Tips for getting the right fit
A ring should slide over the knuckle with a little resistance and sit snugly at the base of the finger without spinning or leaving a deep indent. If your knuckle is noticeably wider than the base, go up half a size and have the ring shaped by a jeweler if it spins. Wide bands (6 mm or more) sit tighter than narrow bands at the same nominal diameter, so order half a size larger. Fingers fluctuate in size throughout the day and with temperature, heat and exercise cause swelling, so measure mid-day for the best balance. When in doubt between two sizes, size up rather than down.
Understanding the EU and German sizing formulas
EU sizing is the most mathematically transparent of all systems. Because circumference equals pi times diameter (C = pi x d), an EU size of 54 corresponds to an inner diameter of 54 / pi = 17.2 mm. German sizing skips the pi step and rounds the diameter directly in millimetres, so a German size 17 corresponds to a 17 mm inner diameter and a circumference of about 53.4 mm. Swiss sizing subtracts 40 from the EU number, a historical convention with no physical meaning beyond giving smaller, tidier numbers. These three continental systems are therefore almost trivially interconvertible once you know one of them.
International ring size conversion chart
| US / Canada | UK / AUS | EU | Germany | Switzerland | Japan / China | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|---|---|
| 3 | F | 44 | 14 | 4 | 4 | 14.1 | 44.3 |
| 3.5 | G | 46 | 15 | 5 | 5 | 14.5 | 45.5 |
| 4 | H | 47 | 15 | 7 | 7 | 14.9 | 46.8 |
| 4.5 | I | 48 | 15 | 8 | 8 | 15.3 | 48.0 |
| 5 | J-K | 49 | 16 | 9 | 9 | 15.7 | 49.3 |
| 5.5 | K | 51 | 16 | 11 | 11 | 16.1 | 50.6 |
| 6 | L | 52 | 17 | 12 | 12 | 16.5 | 51.8 |
| 6.5 | M | 53 | 17 | 13 | 13 | 16.9 | 53.1 |
| 7 | N | 54 | 17 | 14 | 14 | 17.3 | 54.4 |
| 7.5 | O | 56 | 18 | 15 | 15 | 17.7 | 55.6 |
| 8 | P | 57 | 18 | 17 | 17 | 18.1 | 56.9 |
| 8.5 | Q | 58 | 19 | 18 | 18 | 18.5 | 58.1 |
| 9 | R | 59 | 19 | 19 | 19 | 18.9 | 59.4 |
| 9.5 | S | 61 | 19 | 21 | 20 | 19.3 | 60.6 |
| 10 | T | 62 | 20 | 22 | 22 | 19.7 | 61.9 |
| 10.5 | U | 63 | 20 | 23 | 23 | 20.1 | 63.2 |
| 11 | V | 65 | 21 | 24 | 25 | 20.6 | 64.7 |
| 11.5 | W | 66 | 21 | 26 | 26 | 21.0 | 66.0 |
| 12 | X | 67 | 21 | 27 | 27 | 21.4 | 67.2 |
| 12.5 | Y | 69 | 22 | 28 | 28 | 21.8 | 68.5 |
| 13 | Z | 70 | 22 | 29 | 29 | 22.2 | 69.7 |
| 13.5 | Z+1 | 71 | 23 | 31 | 30 | 22.6 | 71.0 |
| 14 | Z+2 | 72 | 23 | 32 | 31 | 23.0 | 72.2 |
| 14.5 | Z+3 | 74 | 23 | 33 | 32 | 23.4 | 73.5 |
| 15 | Z+4 | 75 | 24 | 35 | 33 | 23.8 | 74.7 |
Inside diameter and circumference values are in millimetres. Sizes between half-steps exist but are not shown here.
Frequently asked questions
What is the most common ring size?
For women in the US, the most common ring size is between 5 and 7, with size 6 (EU 52, UK L, diameter 16.5 mm) being the typical average. For men, the most common range is 9 to 10, with size 9 (EU 59, UK R, diameter 18.9 mm) as a frequent reference. These averages vary by region and body size.
How do I convert a UK ring size to a US ring size?
UK ring sizes use letters (F, G, H, ..., Z) while US sizes use numbers. There is no simple arithmetic formula; the conversion depends on a lookup table. As rough benchmarks: UK J is about US 5, UK N is about US 7, UK R is about US 9, and UK T is about US 10. This converter looks up the exact equivalent for you.
What does EU ring size mean?
An EU ring size equals the inner circumference of the ring in millimetres, rounded to the nearest whole number. EU size 54 means the ring has an inner circumference of 54 mm, which corresponds to an inner diameter of about 17.2 mm (since circumference = pi x diameter). This convention is used in France, Russia, Belgium, the Netherlands, and Scandinavia.
How much does a ring size change between half sizes?
Each half US size step corresponds to approximately 0.4 mm in diameter and approximately 1.3 mm in circumference. A full size step is roughly 0.8 mm in diameter and 2.6 mm in circumference. This means the difference between adjacent sizes is very small, which is why measuring precisely in millimetres is so important.
Should I size up or down for a wide band?
Size up for wide bands (typically 6 mm or more). A wider band contacts more of the finger and creates more friction, so it feels tighter than a narrow band at the same nominal diameter. The general guidance is to go up half a size for each additional 3-4 mm of width beyond the standard narrow band.
Can I measure my ring size with a piece of string?
Yes. Wrap a thin strip of paper or a piece of non-stretchy string around the base of the finger you want to measure, mark where the ends overlap, then measure the length of the strip to the mark with a ruler. That measurement in millimetres is your inside circumference, which you can enter into the circumference mode of this converter to find your size in any system.