Ring Size Converter
Convert between US, UK, EU, Australian and Japanese ring sizes instantly — plus an at-home measuring guide.
There's more to your wedding than the logistics.
Explore the free Magic Tools — numerology, astrology, and archetype readings made for the engaged.
Explore the Magic Tools →Ring sizing has five systems and one universal key
Ring sizing confuses people because the systems are not translations of one another. US sizing runs in half and quarter steps, UK and Australian sizing uses letters, European sizing states the ring's internal diameter in millimetres, and Japanese sizing uses its own numbered scale. A single finger therefore carries five different labels, and only one measurement sits underneath them all.
That measurement is circumference, and it is how this converter works. Enter your size in whichever system you already know, or measure your finger at home and enter the millimetres, and you will see the equivalent in all five.
The conversion table
These anchor points cover most adult rings. Circumference is in millimetres, and diameter is the ring's internal measurement, which is what European sizing states.
US 3 / UK F / EU 44 / Australian F / Japanese 4 — 44.2mm circumference, 14.1mm diameter.
US 4 / UK H / EU 47 / Japanese 7 — 46.8mm circumference, 14.9mm diameter.
US 5 / UK J / EU 49 / Japanese 9 — 49.3mm circumference, 15.7mm diameter.
US 6 / UK L / EU 52 / Japanese 12 — 51.9mm circumference, 16.5mm diameter.
US 7 / UK N / EU 54 / Japanese 14 — 54.4mm circumference, 17.3mm diameter.
US 8 / UK P / EU 57 / Japanese 16 — 57.0mm circumference, 18.1mm diameter.
US 9 / UK R / EU 60 / Japanese 18 — 59.5mm circumference, 18.9mm diameter.
US 10 / UK T / EU 62 / Japanese 20 — 62.1mm circumference, 19.8mm diameter.
US 11 / UK V / EU 65 / Japanese 23 — 64.6mm circumference, 20.6mm diameter.
US 12 / UK X / EU 67 / Japanese 25 — 67.2mm circumference, 21.4mm diameter.
US 13 / UK Z+1 / EU 70 / Japanese 27 — 69.7mm circumference, 22.2mm diameter.
Two details catch people out. The UK system continues past Z into Z+1, Z+2 and beyond, so a single letter is not always the whole answer. And the Japanese scale steps unevenly — 4, 5, 7, 8, 9 — so there is no clean arithmetic relationship between Japanese and US sizes.
Measuring at home
If you do not know your size, a strip of paper or a length of non-stretchy string will get you close. Wrap it around the base of the finger you intend to wear the ring on, snug enough that it will not slide off but loose enough to pass over the knuckle. Mark the exact point where the ends meet, lay the strip flat against a ruler and read the length in millimetres. That number is your circumference.
Avoid elastic or stretchy cord, which lengthens as you pull and reads too large. And measure the specific finger — the same person can differ by two full sizes between their left and right hands, and more than that between fingers of the same hand.
Why your size changes through the day
Finger size is not fixed. Fingers swell in warm weather, in the late afternoon and evening, after salty food, after exercise and at altitude, and they shrink in the cold. A ring that feels comfortable at eight in the morning in February can be genuinely uncomfortable at six in the evening in July.
Measure in the evening rather than first thing, at normal indoor temperature. If you land between two sizes in the evening, that is the moment worth paying attention to, because evening is usually the largest your finger gets.
Between two sizes
Size up. A ring that is slightly loose can be worn on another finger temporarily or resized down later, whereas one that is too tight is uncomfortable immediately and may be difficult or impossible to resize upward depending on the band. Eternity bands and heavily pavé-set designs are the hardest to resize at all, which makes getting the size right before ordering far more important for those than for a plain band.
Typical size ranges
For context rather than guidance: the average women's wedding band sits at US size 6 to 7, and the average men's at US size 10 to 11. Ring size does not track with height or body size, so those figures are descriptive rather than predictive — plenty of people sit well outside them, and that is entirely normal.
Frequently asked questions
How do I measure my ring size at home?
Wrap a non-stretchy strip of paper or string around the base of your finger, mark exactly where the ends meet, lay it flat and measure the length in millimetres. That figure is your circumference.
What should I do if I am between two ring sizes?
Size up. A slightly loose ring can be resized down more easily than a tight ring can be resized up, and a tight ring is uncomfortable from the first day.
Why is my ring size different in the morning and the evening?
Fingers swell in warm weather and later in the day. Measure in the evening at normal indoor temperature for the most representative reading.
What size is the average wedding band?
US 6 to 7 for women's bands and US 10 to 11 for men's, though ring size does not correlate with height or body size in any reliable way.
Do US and UK ring sizes use the same numbers?
No. US sizing uses numbers in half steps, while UK and Australian sizing uses letters running from A through Z and then continuing into Z+1, Z+2 and beyond.
Related planning tools
Once you have the size, choose the metal with the Engagement Ring Metal Guide and pair it correctly using the Wedding Band Stack Guide. Decide the style with the Engagement Ring Style Quiz, compare stones using the Diamond Cut Comparison Tool, and keep the whole purchase inside budget with the Jewelry Budget Calculator.