Ring size converter & on-screen ring sizer
A US size 7 ring measures 17.3 mm across and 54.4 mm around — EU 54, about UK N, Japan 14. Enter any size or measurement below to convert between US, UK, EU and Japanese ring sizes, or measure a ring you already own directly on your screen.
Convert a ring size
Conversions use ISO 8653 measurements. UK letters are jeweller approximations — see the note under the full chart.
Measure a ring on your screen
Already own a ring that fits? Rest it on the circle below and read its size. Screens differ, so calibrate first — it takes ten seconds.
Step 1 — Calibrate with a bank card
Hold a bank card, credit card or ID card (they are all 85.60 mm wide) against the bar and drag the slider until the bar is exactly the card's width.
Step 2 — Fit your ring to the circle
Place your ring over the circle and drag the slider until the circle's edge sits exactly on the ring's inside edge. The nearest standard size updates as you drag.
On-screen measuring is a good estimate, not a jeweller's mandrel. For an expensive ring, confirm with a printed sizer or in store.
The full ring size chart
US and Canadian sizes run numerically, EU sizes are the inner circumference in millimetres, the UK and Australia use letters, and Japan uses its own numbering. The complete conversion table is on the ring size chart page; the most common sizes are:
| US / Canada | Inside diameter (mm) | Inside circumference (mm) | EU (ISO 8653) | UK / AU (approx.) | Japan |
|---|---|---|---|---|---|
| 3 | 14.1 | 44.2 | 44 | F | 4 |
| 4 | 14.9 | 46.8 | 47 | H | 7 |
| 5 | 15.7 | 49.3 | 49 | J | 9 |
| 6 | 16.5 | 51.9 | 52 | L | 12 |
| 7 | 17.3 | 54.4 | 54 | N | 14 |
| 8 | 18.1 | 57.0 | 57 | P | 16 |
| 9 | 19.0 | 59.5 | 60 | R | 18 |
| 10 | 19.8 | 62.1 | 62 | T | 20 |
| 11 | 20.6 | 64.6 | 65 | V | 23 |
| 12 | 21.4 | 67.2 | 67 | X | 25 |
| 13 | 22.2 | 69.7 | 70 | Z | 27 |
EU sizes follow ISO 8653, where the size number is the ring's inner circumference in millimetres. UK letter sizes are the widely used jeweller approximations and may differ slightly from one jeweller to another. Half sizes between whole sizes are interpolated.
How the four systems relate
US / Canada sizes step by roughly 0.8 mm of diameter per full size. EU sizes are the most literal: under ISO 8653 the number is the inner circumference in millimetres, so converting is just measuring around the inside of the band. UK / AU sizes use letters from A to Z; they track the same measurements but the letter steps are a jeweller's convention rather than a formula, which is why charts differ slightly. Japanese sizes are numbers roughly equal to the US size plus 7 in the common range, defined from the same millimetre measurements.
Buying for someone else? Start from the average ring sizes, or use the dedicated charts for women and men. No ring to measure? The paper-strip method needs nothing but paper and a ruler.
Frequently asked questions
What is a US size 7 ring in mm?
A US size 7 ring has an inside diameter of 17.3 mm and an inside circumference of 54.4 mm. That is EU size 54 under ISO 8653, roughly a UK size N, and a Japanese size 14.
How do EU ring sizes work?
EU ring sizes follow ISO 8653: the size number is simply the ring's inner circumference in millimetres. A ring measuring 57.0 mm around the inside is an EU 57, which converts to a US size 8.
Are UK ring sizes exact?
UK sizes use letters (F, G, H…) and are approximations — the letter steps are not perfectly uniform and individual jewellers can differ by a fraction of a size. Treat a converted UK letter as a starting point and confirm against the jeweller's own chart.
Can I measure my ring size on a phone screen?
Yes, if you calibrate first. Screen pixels are not a fixed physical size, so this page asks you to match an on-screen bar to a standard bank card (85.60 mm) before showing the ring circle. After calibration the circle is drawn at true size and you can rest a ring you already own on it.
What if I am between two sizes?
Most jewellers advise choosing the larger size, especially for wide bands, which fit tighter than narrow ones. Fingers also swell slightly during the day, so measure in the evening for the most generous reading.