How to use it
- Choose what you know: US size, diameter, circumference, EU or UK size.
- Enter the value to see every other system.
- Or open the on-screen sizer and calibrate it with a credit card.
- Lay a ring on the circle and adjust until it matches.
Ring size chart
| US size | Inside diameter | Inside circumference | EU | UK |
|---|---|---|---|---|
| 4 | 14.9 mm (0.586 in) | 46.8 mm | 47 | H½ |
| 5 | 15.7 mm (0.618 in) | 49.3 mm | 49 | J½ |
| 6 | 16.5 mm (0.650 in) | 51.9 mm | 52 | L½ |
| 7 | 17.3 mm (0.682 in) | 54.4 mm | 54 | N½ |
| 8 | 18.1 mm (0.714 in) | 57.0 mm | 57 | P½ |
| 9 | 18.9 mm (0.746 in) | 59.5 mm | 60 | R½ |
| 10 | 19.8 mm (0.778 in) | 62.1 mm | 62 | T½ |
| 11 | 20.6 mm (0.810 in) | 64.6 mm | 65 | V½ |
| 12 | 21.4 mm (0.842 in) | 67.2 mm | 67 | X½ |
The tool shows a full chart in quarter and half sizes, with Japanese and Italian/Spanish/Swiss sizes too, and highlights the row nearest to your entry.
How US, UK and EU sizes work
- US and Canada: inside diameter = 0.458 in + 0.032 in × size (11.63 mm + 0.8128 mm × size). Each whole size adds about 0.8 mm of diameter; quarter and half sizes are common.
- EU (ISO 8653): the inside circumference in millimeters, so a size 54 ring is 54 mm around inside.
- UK and Australia: letters, A to Z, with half sizes, about 1.25 mm of circumference apart.
- Japan: a numbered scale roughly equal to circumference − 40 mm (approximate).
- Italy, Spain, Switzerland: circumference − 40.
Sizes vary slightly between charts, so for an expensive ring confirm with the jeweler's own sizer.
Measure a ring on your screen
Open Measure a ring you own on the screen:
- Calibrate: hold a credit or debit card (a standard ID-1 card, 85.60 × 53.98 mm) against the screen and move the slider until the green bar is exactly the card's width. On a phone, use the short side. The browser remembers the calibration on that device.
- Measure: lay a ring that fits on the circle and adjust it until the circle's edge meets the inside edge of the ring. Click Use this size.
After calibration the on-screen sizer is accurate to about ±0.2–0.3 mm, roughly a quarter size.
Measuring your finger
- Wrap a strip of paper or string around the base of the finger, mark where it overlaps, and measure the length in mm: that's the circumference (and the EU size).
- Measure at the end of the day, when fingers are largest, and not when cold.
- The ring must pass over the knuckle; if your knuckle is large, measure it too and pick a size in between.
- Wide bands (over about 6 mm) fit tighter, so go up a quarter or half size.
- Between two sizes, choose the larger one.
Frequently asked questions
What ring size is 17 mm?
A 17 mm inside diameter is about US 6½ (EU 53, UK M½). Enter the exact diameter in the calculator.
How do I convert a UK ring size to US?
Choose UK letter, type the size (for example N or N½), and read the US size. UK N½ is about US 7.
Is EU ring size the same as circumference?
Yes. The EU (ISO 8653) size is the inside circumference in millimeters.
How accurate is the on-screen ring sizer?
About ±0.2–0.3 mm after calibration with a card. For an engagement ring, confirm with a jeweler.
What if I'm between sizes?
Pick the larger size, especially for wide bands or if your knuckle is large.
Last updated: November 12, 2026