Ring Size Calculator
Convert ring measurements between US, UK, and EU sizes from diameter or circumference.
By Konstantin Iakovlev · Updated September 2026 · Source: ISO 8653:2016 Jewellery - Ring-sizes - Definition, measurement and designation
US Size
6.5
UK Size
M½
EU Size
53.2
Size Equivalents
| US Size | 6.5 |
| UK Size | M½ |
| EU Size (circumference mm) | 53.2 |
| Inside Diameter | 16.92 mm |
| Inside Circumference | 53.16 mm |
Reference Chart
| US | UK | EU | Diameter | Circ. |
|---|---|---|---|---|
| 3 | F | 44.1 | 14.05 mm | 44.14 mm |
| 4 | H | 46.7 | 14.86 mm | 46.68 mm |
| 5 | J | 49.3 | 15.70 mm | 49.32 mm |
| 6 | L½ | 51.9 | 16.51 mm | 51.87 mm |
| 7 | N½ | 54.5 | 17.35 mm | 54.51 mm |
| 8 | P½ | 57.2 | 18.19 mm | 57.15 mm |
| 9 | R | 59.3 | 18.89 mm | 59.34 mm |
| 10 | T½ | 62.3 | 19.84 mm | 62.33 mm |
| 11 | V½ | 65.0 | 20.68 mm | 64.97 mm |
| 12 | Y | 67.5 | 21.49 mm | 67.51 mm |
| 13 | Z+1 | 70.2 | 22.33 mm | 70.15 mm |
| 14 | Z+2½ | 72.3 | 23.01 mm | 72.29 mm |
| 15 | Z+4½ | 74.8 | 23.83 mm | 74.84 mm |
Use the Ring Size Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only. Results are estimates based on the information you provide and the assumptions described on this page.
How It Works
Ring sizing runs on different standards in the US, UK, and EU, and converting between them is straightforward once you have either the band's diameter or its circumference. A wrong size means a return or a resize, so it pays to get the fit right the first time.
The calculator holds a table of US sizes 3 to 15 in half sizes, each with its inside diameter and inside circumference. The two are linked by C = πD; going the other way, D = C/π. Whatever you enter, a diameter, a circumference or a US size, is matched to the nearest half size in that table. The EU size shown is that size's inside circumference in millimeters, which is how ISO 8653 designates ring sizes.
Measure with a flexible tape or a length of string, snug against the finger without pinching. Finger size drifts over the course of a day and with temperature, so the most reliable reading comes in the evening when fingers tend to be warmest. Resist the urge to round too hard, because even a fraction of a millimeter can push you into a different ring size entirely.
Example: Converting a Circumference to US and EU Sizes
- 1 You have a ring that measures 56.5 mm around the inside.
- 2 Choose Circumference (mm) and enter 56.5. The nearest sizes in the table are US 7.5 (55.76 mm) and US 8 (57.15 mm); 56.5 is 0.65 mm from US 8 and 0.74 mm from US 7.5, so the calculator picks US 8.
- 3 The calculator outputs: US size 8, inside diameter 18.19 mm, inside circumference 57.15 mm, EU size 57.2.
- 4 Because 56.5 mm falls between two half sizes, try both on if you can, or ask a jeweler whether a quarter size is available; the calculator itself works in half sizes.
Source: ISO 8653:2016 Jewellery - Ring-sizes - Definition, measurement and designation · Last updated: September 2026
Frequently Asked Questions
How do I find my ring size at home?
What is the most common ring size for women?
How do US ring sizes convert to European sizes?
You might also need
Cost of Living Comparison — Salary Equivalency by US City
Compare cost of living between US cities and see the salary needed to maintain your lifestyle when relocating. Free, instant results for any US metro area.
Tip Calculator
Calculate tip amount and split the bill between multiple people. Quick preset tip percentages for restaurants and services.
Discount Calculator
Calculate sale price after discount with optional sales tax. Supports stacked percentage discounts.