Ring Size Converter
Know a diameter in mm, a circumference, or a size in one system — read every other system.
All conversion runs locally — nothing is uploaded.
Converted size
Pick a measurement type, enter the value and convert.
Full Ring Size Chart
Anchored to inside diameter in mm — ISO 8653 for EU (size = circumference), the US trade scale, UK letters, JIS numbering for Japan. HK values are the common circumference-minus-40 convention.
| Diameter (mm) | Circumf. (mm) | US / CA | UK / AU | EU / ISO | Japan | HK (ref) |
|---|---|---|---|---|---|---|
| 14.1 | 44.2 | 3 | F | 44 | 4 | 4 |
| 14.5 | 45.5 | 3.5 | G | 45 | 5 | 6 |
| 14.9 | 46.8 | 4 | H | 47 | 7 | 7 |
| 15.3 | 48.0 | 4.5 | I | 48 | 8 | 8 |
| 15.7 | 49.3 | 5 | J | 49 | 9 | 9 |
| 16.1 | 50.6 | 5.5 | K | 50 | 10 | 11 |
| 16.5 | 51.9 | 6 | L | 52 | 12 | 12 |
| 16.9 | 53.1 | 6.5 | M | 53 | 13 | 13 |
| 17.3 | 54.4 | 7 | N | 54 | 14 | 14 |
| 17.7 | 55.7 | 7.5 | O | 56 | 15 | 16 |
| 18.1 | 57.0 | 8 | P | 57 | 16 | 17 |
| 18.5 | 58.3 | 8.5 | Q | 58 | 17 | 18 |
| 19.0 | 59.5 | 9 | R | 59 | 18 | 20 |
| 19.4 | 60.8 | 9.5 | S | 61 | 19 | 21 |
| 19.8 | 62.1 | 10 | T | 62 | 20 | 22 |
| 20.2 | 63.4 | 10.5 | U | 63 | 22 | 23 |
| 20.6 | 64.6 | 11 | V | 64 | 23 | 25 |
| 21.0 | 65.9 | 11.5 | W | 66 | 24 | 26 |
| 21.4 | 67.2 | 12 | X | 67 | 25 | 27 |
| 21.8 | 68.5 | 12.5 | Y | 68 | 26 | 28 |
| 22.2 | 69.7 | 13 | Z | 69 | 27 | 30 |
Three Ways to Measure at Home
- Existing ring: measure the inside diameter of a ring that fits, straight across the middle — the most reliable method.
- Paper strip: wrap a thin strip snugly around the finger base, mark the overlap, measure the length in mm — that is the circumference.
- Measure in the evening when fingers are largest; a good ring passes the knuckle with slight resistance and sits without squeezing.
Frequently Asked Questions
A ring with 17 mm inner diameter is which US size?
An inside diameter of about 17.3 mm is US 7 (UK N, EU 54, JP 14). A 16.9 mm diameter is US 6.5. 17 mm sits between the two — most people take US 7.
How do EU ring sizes work?
Under ISO 8653 the EU size equals the inner circumference in millimetres: a size 54 ring has a 54 mm inner circumference — about 17.2 mm diameter.
How do I measure my ring size without a sizer?
Wrap a thin paper strip snugly around the finger base, mark where it overlaps and measure the length in mm — that is your circumference. Or measure the inside diameter of a ring that already fits.
Should a wide band ring be bigger?
Yes — bands around 6 mm or wider usually need half a size up because more finger surface is covered. Thin stacking bands can go true to size or even down half.
Is the Hong Kong size the same as mainland China?
They are close but not identical conventions — both are roughly circumference-based. The HK column here is the common circumference-minus-40 reference; mainland jewellers may use their own chart, so confirm with the seller.
Chart values are references anchored to inside diameter. Wide bands (6 mm+) usually need half a size up. Tables use the open MySizeCharts data set (CC BY 4.0) and published standards. · Size data · Read our fashion coverage