💍 Ring Size Converter
Convert ring sizes between US, EU (mm circumference), Japan, and diameter in millimeters. Includes a measuring guide and international size reference chart.
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Common Ring Size Conversions
| Input | Unit | Result | Unit |
|---|---|---|---|
| 5 | US / Canada Ring Size | 49.260173 | EU / Int'l (circumference mm) |
| 7 | US / Canada Ring Size | 54.487783 | EU / Int'l (circumference mm) |
| 6 | US / Canada Ring Size | 11 | Japan / Asia Ring Size |
| 52 | EU / Int'l (circumference mm) | 6.048214 | US / Canada Ring Size |
| 13 | Japan / Asia Ring Size | 7 | US / Canada Ring Size |
| 7 | US / Canada Ring Size | 17.344 | Diameter (mm) |
Popular Conversions
Formula Reference
Ring size conversion formulas (approximate): EU (mm circ.) = diameter_mm × π diameter_mm = 11.52 + US × 0.832 (±0.1 mm) JP size ≈ US × 2 − 1 (exact for integer sizes) Common size reference: US 5 = EU 49.3 = JP 9 = 15.7 mm diameter US 6 = EU 51.8 = JP 11 = 16.5 mm diameter US 7 = EU 54.4 = JP 13 = 17.3 mm diameter US 8 = EU 57.0 = JP 15 = 18.2 mm diameter US 9 = EU 59.5 = JP 17 = 18.9 mm diameter US 10 = EU 62.1 = JP 19 = 19.8 mm diameter UK ring sizes use letters (F–Z) — UK A ≈ US 2.5, adding ~0.5 US per letter. UK F = US 3 • UK J = US 5 • UK N = US 7 • UK T = US 10
About Ring Size Conversions
Ring sizing varies significantly between countries. The US and Canada use numeric sizes from about 3 to 13, with half and quarter sizes available. EU and international sizing uses the inner circumference of the ring in millimeters — a size 52 ring has an inner circumference of 52 mm. Japanese sizing runs from 1 to 30 and corresponds roughly to the US size doubled minus 1.
To measure your ring size at home, wrap a thin strip of paper or string around the base of your finger, mark where it overlaps, then measure the length in millimeters — that is your EU size. Divide the circumference by π (3.14159) to get the inner diameter. Fingers change size with temperature and time of day; measure in the afternoon when fingers are at their largest, and take several measurements before ordering.
All conversions on this page are approximate. Minor differences between brands and jewelers are common — ring sizing is not standardized globally, and the same number can represent slightly different dimensions depending on the country and manufacturer. For important purchases like engagement rings, have a jeweler measure your finger in person.
Frequently Asked Questions
How do I measure my ring size at home?
Wrap a thin strip of paper or soft string around the base of your finger. Mark where it overlaps without squeezing. Lay it flat and measure the length in millimeters — that is your EU ring size (inner circumference). Divide by π (3.14159) to get inner diameter in mm. For US size, use the converter above. Measure in the afternoon when fingers are slightly larger.
What is a US ring size 7 in EU?
US ring size 7 is approximately EU 54.4 mm (inner circumference). This converts to about 17.3 mm inner diameter. In Japan, US 7 corresponds to approximately JP size 13.
How do US and UK ring sizes compare?
UK ring sizes use letters instead of numbers. The correspondence is approximate: UK F ≈ US 3, UK H ≈ US 4, UK J ≈ US 5, UK L ≈ US 6, UK N ≈ US 7, UK R ≈ US 9, UK T ≈ US 10. Each letter in the UK system roughly corresponds to half a US size increment. UK sizes go up to Z and Z+2 for the largest sizes.
Why is the EU ring size a number in the 40s to 70s?
EU ring sizes represent the inner circumference of the ring in millimeters. A ring that fits your finger has an inner circumference approximately equal to your finger's circumference. A typical adult woman might have a finger circumference of 50–54 mm, while a typical adult man might be 60–65 mm. This direct millimeter measurement is more precise than a numbered system.
Do ring sizes vary between jewelers?
Yes, slightly. There is no single global standard for ring sizing, so a US size 7 from one jeweler may be fractionally different from a US 7 from another. This is especially relevant for rings that cannot be resized, such as those with stones around the full band. For any significant purchase, have your finger measured by a professional jeweler using physical sizing rings.
Related Guides
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Sources
Our Methodology
How we source and verify conversion factors.
Reference Library
Tables, charts, and authoritative reference data.
All Converters
All conversion results are provided for general informational purposes only. Our formulas use internationally recognized conversion factors; however, rounding may affect precision. Do not rely on these results for professional, medical, legal, or engineering decisions without independent verification. Read our full disclaimer.