Ring size measure and convert
1 · Calibrate your screen
Hold a bank card against the screen and resize the drawn card until it matches exactly. Every bank card is 85.60 × 53.98 mm.
2 · Measure a ring
Lay a ring that fits flat on the circle and resize the circle until its edge meets the inside of the ring.
US, Canada
7
| System | Size |
|---|---|
| US, Canada | 7 |
| ISO / Europe (mm) | 54 |
| Diameter (DE, NL) | 17.25 mm |
| UK, Australia | N½ |
| Italy, Spain, Switzerland | 14 |
| Japan | 14 |
| Brazil | 14 |
Japanese sizes follow a common jewellers' rule that drifts above size 21; Brazilian sizes follow jewellers' charts. When in doubt, ask the jeweller.
Two steps: calibrate the screen once with a bank card, then lay a ring that fits on the circle. You can also wrap a strip of paper around your finger, measure it and type the circumference.
Fingers swell in the heat and at the end of the day: measure in the afternoon at room temperature, and pick the larger size between two.
Questions
How do I measure my ring size at home?
Calibrate the screen with a bank card, then lay a ring that fits on the circle and resize it until it meets the inside edge. The size appears in every system.
What is a US size 7 ring in mm?
About 17.3 mm inside diameter, 54.4 mm circumference: size 54 in Europe, N½ in the UK, 14 in Italy.
Why calibrate with a bank card?
Screens differ: the browser does not know how big a millimetre is on yours. A bank card is 85.60 mm wide everywhere, so it gives the true scale.
Is the on-screen measure accurate?
To within about half a size once calibrated. For an expensive ring, confirm with a jeweller's ring gauge.