Ring Size Converter
US, UK, EU and Japan sizes from mm
Find Your Size
Wrap string or paper around your finger and enter the length under 'Circ. mm'
Ring size
US 7
Japan / Korea14
US / Canada7
UK / AustraliaN½
Europe (EU / ISO)54
Inner diameter17.32 mm
Inner circumference54.4 mm
Ring Size Chart
| US | Dia. mm | Circ. mm | UK | EU | JP/KR |
|---|---|---|---|---|---|
| 3 | 14.07 | 44.2 | F | 44 | 4 |
| 3½ | 14.48 | 45.5 | G | 45 | 5 |
| 4 | 14.88 | 46.8 | H | 47 | 7 |
| 4½ | 15.29 | 48.0 | I | 48 | 8 |
| 5 | 15.70 | 49.3 | J | 49 | 9 |
| 5½ | 16.10 | 50.6 | K | 51 | 10 |
| 6 | 16.51 | 51.9 | L½ | 52 | 12 |
| 6½ | 16.92 | 53.1 | M½ | 53 | 13 |
| 7 | 17.32 | 54.4 | N½ | 54 | 14 |
| 7½ | 17.73 | 55.7 | O½ | 56 | 15 |
| 8 | 18.14 | 57.0 | P½ | 57 | 16 |
| 8½ | 18.54 | 58.3 | Q½ | 58 | 18 |
| 9 | 18.95 | 59.5 | R½ | 60 | 19 |
| 9½ | 19.35 | 60.8 | S½ | 61 | 20 |
| 10 | 19.76 | 62.1 | T½ | 62 | 21 |
| 10½ | 20.17 | 63.4 | U½ | 63 | 23 |
| 11 | 20.57 | 64.6 | V½ | 65 | 24 |
| 11½ | 20.98 | 65.9 | W½ | 66 | 25 |
| 12 | 21.39 | 67.2 | X½ | 67 | 26 |
| 12½ | 21.79 | 68.5 | Y½ | 68 | 27 |
| 13 | 22.20 | 69.7 | Z½ | 70 | 29 |
Japanese and Korean sizes start at 13.0 mm inner diameter for size 1 and grow about 1/3 mm per size. EU/ISO size equals the inner circumference in mm. Brands vary slightly — always check the retailer's mm chart.
How to Measure Your Finger
| Step | How |
|---|---|
| 1 | Wrap string or a thin paper strip once around the base of the finger |
| 2 | Mark where it overlaps and measure the length in mm |
| 3 | Choose 'Circ. mm' above and enter the length |
| 4 | If your knuckle is larger, check that the ring will pass over it |
Fingers swell in the evening and in heat and shrink in the cold. Measure 2–3 times a day and go up a half size for bands wider than 6 mm.
Formulas & Sources
- Japan / Korea: inner diameter = 13.0 + (size − 1) ÷ 3 mm
- US: inner diameter (in) = 0.458 + 0.032 × size · EU (ISO 8653): inner circumference in mm · UK: 37.8 mm at A, +1.25 mm per letter
- Brands can differ by about half a size
Last reviewed: 2026-10-19
FAQ
How do I find my ring size at home?
Wrap string or paper around your finger, measure the length in mm and enter it under 'Circ. mm'. A 54 mm circumference is about a US 6¾.
What is a US size 7 in other systems?
US 7 is about 17.3 mm inner diameter: UK N½, EU 54, Japan/Korea 14.
How big is one US ring size?
Each full US size adds 0.8128 mm (1/32 inch) to the inner diameter, about 2.55 mm in circumference.
What is the EU ring size?
EU (ISO 8653) sizes are the inner circumference in millimeters, so size 54 has a 54 mm inner circumference.
Should I size up for a wide band?
Yes — for bands wider than about 6 mm, go up a quarter to half size for comfort.