💍 Ring Size Converter
Convert ring sizes between US, UK letters, EU/ISO, Japanese and Swiss sizes, or find yours from a diameter, a circumference or an on-screen ring sizer.
Sizes are rounded to the nearest size each system uses: quarter sizes (US), half letters (UK) and whole numbers (EU, Japan). Jewelers’ charts can differ by a fraction of a size.
Ring size chart
| US | UK | EU | Japan | Diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 14.1 mm | 44.2 mm |
| 3½ | G½ | 45 | 5 | 14.5 mm | 45.5 mm |
| 4 | H½ | 47 | 7 | 14.9 mm | 46.8 mm |
| 4½ | I½ | 48 | 8 | 15.3 mm | 48.0 mm |
| 5 | J½ | 49 | 9 | 15.7 mm | 49.3 mm |
| 5½ | K½ | 51 | 10 | 16.1 mm | 50.6 mm |
| 6 | L½ | 52 | 12 | 16.5 mm | 51.9 mm |
| 6½ | M½ | 53 | 13 | 16.9 mm | 53.1 mm |
| 7 | N½ | 54 | 14 | 17.3 mm | 54.4 mm |
| 7½ | O½ | 56 | 15 | 17.7 mm | 55.7 mm |
| 8 | P½ | 57 | 16 | 18.1 mm | 57.0 mm |
| 8½ | Q½ | 58 | 18 | 18.5 mm | 58.2 mm |
| 9 | R½ | 60 | 19 | 18.9 mm | 59.5 mm |
| 9½ | S½ | 61 | 20 | 19.4 mm | 60.8 mm |
| 10 | T½ | 62 | 21 | 19.8 mm | 62.1 mm |
| 10½ | U½ | 63 | 22 | 20.2 mm | 63.3 mm |
| 11 | V½ | 65 | 24 | 20.6 mm | 64.6 mm |
| 11½ | W½ | 66 | 25 | 21.0 mm | 65.9 mm |
| 12 | X½ | 67 | 26 | 21.4 mm | 67.2 mm |
| 12½ | Z | 68 | 27 | 21.8 mm | 68.5 mm |
| 13 | Z+1 | 70 | 29 | 22.2 mm | 69.7 mm |
| 13½ | Z+2 | 71 | 30 | 22.6 mm | 71.0 mm |
| 14 | Z+3 | 72 | 31 | 23.0 mm | 72.3 mm |
Measure a ring on your screen
Step 1: hold the short edge of a bank card (53.98 mm) against the blue bar and drag the slider until the bar is exactly as long as the card. Step 2: lay a ring that fits on the circle and adjust until the circle just fills the inside edge.
What Ring Size Converter Does
This ring size converter translates a ring size between the US and Canadian number scale, UK and Australian letters, EU and ISO sizes, Japanese sizes and Swiss sizes. You can also start from a measurement — the inside diameter or inside circumference of a ring in millimeters or inches — and see the size in every system at once, with a full chart from US 3 to 14.
No ring sizer at hand? The on-screen sizer uses a bank card to calibrate your display, then lets you match a circle to the inside of a ring you already own. Every system is converted through the ring’s inside diameter using its defining formula, so the results agree with one another rather than being copied from a chart.
How to Use Ring Size Converter
- Choose the system you know, or a measurement type
- Enter your size, or the diameter or circumference
- Read the size in US, UK, EU, Japanese and Swiss systems
- Find neighboring sizes in the ring size chart
- Or calibrate with a bank card and match the on-screen circle to a ring
Formula Used by Ring Size Converter
Converting through the inside diameter
US: d = 11.63 + 0.8128 × size · UK: circumference = 37.5 + 1.25 × letter number (A = 0) · EU = circumference · Japan: d = 13 + (size − 1) ÷ 3 · Swiss = circumference − 40
- d
- Inside diameter in mm
- circumference
- Inside circumference in mm = π × d
Worked example
A US size 7.
- d = 11.63 + 0.8128 × 7 = 17.32 mm
- Circumference = π × 17.32 = 54.4 mm
- UK: (54.4 − 37.5) ÷ 1.25 = 13.5 → N½
- Japan: (17.32 − 13) × 3 + 1 = 14
Result: US 7 = UK N½ = EU 54 = Japan 14 = Swiss 14.5.
From a paper strip
Circumference = length of the strip (mm) · diameter = circumference ÷ π
Worked example
A strip that measures 57 mm around the finger.
- d = 57 ÷ π = 18.14 mm
- US: (18.14 − 11.63) ÷ 0.8128 = 8.0
- UK: (57 − 37.5) ÷ 1.25 = 15.6 → P½
Result: US 8 = UK P½ = EU 57.
Ring Size Chart
| US & Canada | UK & Australia | EU / ISO | Japan | Inside diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 14.1 mm | 44.2 mm |
| 4 | H½ | 47 | 7 | 14.9 mm | 46.8 mm |
| 5 | J½ | 49 | 9 | 15.7 mm | 49.3 mm |
| 6 | L½ | 52 | 12 | 16.5 mm | 51.9 mm |
| 7 | N½ | 54 | 14 | 17.3 mm | 54.4 mm |
| 8 | P½ | 57 | 16 | 18.1 mm | 57.0 mm |
| 9 | R½ | 60 | 19 | 19.0 mm | 59.5 mm |
| 10 | T½ | 62 | 21 | 19.8 mm | 62.1 mm |
| 11 | V½ | 65 | 24 | 20.6 mm | 64.6 mm |
| 12 | X½ | 67 | 26 | 21.4 mm | 67.2 mm |
| 13 | Z+1 | 70 | 29 | 22.2 mm | 69.7 mm |
Ring Sizing Systems
| System | Based on | Step between sizes |
|---|---|---|
| US & Canada | Inside diameter | 0.8128 mm (0.032 in), with quarter sizes |
| UK, Ireland & Australia | Inside circumference (BS 6820) | 1.25 mm per letter, with half sizes |
| EU / ISO 8653 | Inside circumference in mm | 1 mm |
| Japan | Inside diameter | ⅓ mm |
| Switzerland | Inside circumference − 40 mm | 1 mm |
How to Read Your Result
Measuring for an accurate fit
Fingers are larger when warm and later in the day, and smaller when cold. Measure a few times at different times of day, and make sure the ring will pass over your knuckle — if the knuckle is much larger than the base of the finger, size for the knuckle.
Wide bands and comfort fit
A wide band fills more of the finger, so it feels tighter than a thin band of the same size; many jewelers suggest going up a quarter to half size for bands about 6 mm or wider. Comfort-fit bands, rounded on the inside, tend to feel roomier than flat-inside bands of the same size.
Using the on-screen sizer
Screens differ in pixel density, so calibrate first: payment cards follow the ID-1 format of 85.60 × 53.98 mm, and the sizer uses the 53.98 mm short edge. Match the circle to the inside edge of the ring, not the outside, and confirm with a second measurement before ordering.
Limitations & Accuracy Notes
- Jewelers’ charts can differ by a quarter size or half a letter because of rounding and manufacturing tolerances.
- Some rings, such as full eternity bands and tungsten rings, cannot easily be resized — measure carefully before ordering them.
- The on-screen sizer is only as accurate as its calibration; use a physical ring sizer for an engagement ring or other important purchase.