Secret Ring SizeSizes in units
Ring size in mm, cm and inches
A US 7 ring is 17.3 mm (0.68 inches) across the inside and 54.4 mm (5.44 cm, 2.14 inches) around. Pick any size to see its numbers, or type a measurement to get the size.
A size in every unit
- Inside diameter
- Circumference
Or a measurement to a size
Right on a size.
Screens, paper and string can be off by a little. Before you order, tell the jeweler how you measured and ask about resizing.
Common sizes at a glance
| US | Across, mm | Across, in | Around, cm | Around, in |
|---|---|---|---|---|
| 5 | 15.7 | 0.62 | 4.93 | 1.94 |
| 6 | 16.5 | 0.65 | 5.19 | 2.04 |
| 7 | 17.3 | 0.68 | 5.44 | 2.14 |
| 8 | 18.1 | 0.71 | 5.70 | 2.24 |
| 9 | 18.9 | 0.75 | 5.95 | 2.34 |
| 10 | 19.8 | 0.78 | 6.21 | 2.44 |
| 11 | 20.6 | 0.81 | 6.46 | 2.54 |
| 12 | 21.4 | 0.84 | 6.72 | 2.64 |
The US scale starts at 11.63 mm for size 0 and adds 0.8128 mm across for each full size. So a 17 mm ring works out to size 6.6, close enough to US 6½ (16.9 mm) that the tool reads it as 6½; a 16 mm ring reads US 5½. Circumference is the diameter times 3.1416.
Measuring a finger rather than a ring? Use string or paper. For UK and EU sizes, use the ring size converter.
Questions
What ring size is 17 mm?
A 17 mm inside diameter is a US 6½, whose inside is 16.9 mm. If 17 mm is the length around, that is far too small for an adult ring: check the measurement.
What is a size 7 ring in mm?
17.3 mm across the inside and 54.4 mm around.
How many cm is a size 6 ring?
5.19 cm around the inside, and 1.65 cm across.
Is ring size the diameter or the circumference?
Both describe the same size. US and UK sizes are labels; the diameter is measured across the inside of a ring, and the circumference around a finger.