How the Ring Size Calculator Works
This tool converts inner diameter or finger circumference into ring sizes in Italian, US, and UK systems. Enter either measurement to get all conversions.
How to Measure Your Finger
Method 1 -- With an existing ring: Take a ring that fits well and measure the inner diameter with a ruler in millimeters.
Method 2 -- With string or paper: Wrap a thin string or paper strip around the base of your finger, mark the overlap, and measure the length. This is the circumference.
Size Systems
- US: Numeric scale from 3 to 13, in half-size increments, based on diameter
- UK: Alphabetical scale from A to Z, each letter corresponding to a specific circumference
- Italy/Europe: Based on circumference in mm minus 40
Quick Conversion Table
| Diameter (mm) | Circ. (mm) | IT | US | UK |
|---|---|---|---|---|
| 15.3 | 48 | 8 | 4.5 | H |
| 16.5 | 52 | 12 | 6 | L |
| 17.3 | 54 | 14 | 7 | N |
| 18.2 | 57 | 17 | 8 | P |
| 19.1 | 60 | 20 | 9 | S |
Tips for Accurate Measurement
- Fingers change size throughout the day (larger in evening, smaller in morning)
- Heat expands, cold contracts: measure at room temperature
- The dominant hand is slightly larger
- When in doubt, choose the slightly larger size