Ring Size Converter
Convert ring sizes between US, UK, EU, and Japanese systems or calculate from finger diameter in mm.
Returns all international equivalents.
Ring sizing systems differ by country, and even within a single country there can be variation between jewelers. The most universally reliable measurement is the circumference of your finger in millimeters — every sizing system can be derived from this single measurement.
How to measure your finger at home:
- Cut a thin strip of paper about 3/4" (2 cm) wide and 4 inches (10 cm) long
- Wrap it snugly (but not tightly) around the base of the finger you wish to size
- Mark where the paper overlaps with a pen
- Measure the distance from the end of the paper to your mark in millimeters
- That measurement is your finger circumference
Best time to measure: Late afternoon or evening — fingers are slightly larger due to normal swelling. Avoid measuring when cold — cold fingers shrink and may give a size too small. For knuckle-heavy fingers (where the knuckle is much wider than the base), measure at the widest part.
Ring size conversion chart:
| Circumference (mm) | Diameter (mm) | US | UK | EU | Japan |
|---|---|---|---|---|---|
| 44.2 | 14.1 | 3 | F | 44 | 3 |
| 46.8 | 14.9 | 4 | H | 47 | 6 |
| 49.3 | 15.7 | 5 | J | 49 | 9 |
| 51.9 | 16.5 | 6 | L | 52 | 12 |
| 54.4 | 17.3 | 7 | N | 54 | 14 |
| 57.0 | 18.1 | 8 | P | 57 | 17 |
| 59.5 | 18.9 | 9 | R | 60 | 20 |
| 62.1 | 19.8 | 10 | T | 62 | 22 |
| 64.6 | 20.6 | 11 | V | 65 | 25 |
| 67.2 | 21.4 | 12 | X | 67 | 27 |
| 69.7 | 22.2 | 13 | Z | 70 | 30 |
Diameter from circumference:
Diameter = Circumference / π (≈ Circumference / 3.1416)
System notes:
- US sizes use numbers with half sizes (5, 5.5, 6, 6.5…)
- UK sizes use letters (A–Z with half sizes like Z+1, Z+2)
- EU sizes are the finger circumference in millimeters, rounded to the nearest whole number
- Japanese sizes use a different numerical scale starting from size 1
Ring width consideration: Wider bands (6mm+) fit more snugly than narrow bands (2–3mm). If ordering a wide-band ring, consider sizing up by half a US size for comfort.
Online ordering tip: When buying a ring online without trying it on, order the most commonly suggested size for that finger and region. Average US women’s ring size: 6–7 (US) Average US men’s ring size: 10–11 (US) These are averages only — individual variation is significant.
Always consult a local jeweler for precise sizing before purchasing a non-resizable ring or an expensive piece.