Utility Loft → Ring Size Converter
Ring Size Converter
Enter one measurement — a ring's inside diameter, your finger's circumference, or a size you already know — and get the match in US, UK, Europe, Japan, and millimeters.
Enter a measurement above to see your size in every standard.
Tip: measure at the end of the day, and if you're between sizes, round up.
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How to measure your ring size
📏 From a ring that fits
Place a ring you already wear on a millimeter ruler and measure straight across theinside edge — that's the inside diameter. Enter it in theinside diameter tab above. This is the most accurate home method.
🧵 From your finger
Wrap a thin strip of paper or string snugly around the base of your finger. Mark the overlap, lay it flat against a ruler, and measure the length in millimeters. Enter it in the finger circumference tab.
Ring size conversion chart
Every standard side by side. Inside circumference (mm) is the physical measurement each size maps to.
| US / CA | UK / AU | Europe | Japan | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.1 | 44.2 |
| 4 | H½ | 47 | 7 | 14.9 | 46.8 |
| 5 | J½ | 49 | 9 | 15.7 | 49.3 |
| 6 | L½ | 52 | 11 | 16.5 | 51.9 |
| 7 | N½ | 54 | 13 | 17.3 | 54.4 |
| 8 | P½ | 57 | 16 | 18.1 | 57.0 |
| 9 | R½ | 59½ | 18 | 19.0 | 59.5 |
| 10 | T½ | 62 | 20 | 19.8 | 62.1 |
| 11 | V½ | 65 | 23 | 20.6 | 64.6 |
| 12 | Y | 67½ | 25 | 21.4 | 67.2 |
| 13 | Z+1 | 70 | 27 | 22.2 | 69.7 |
Half sizes are supported in the converter above. Values are industry-standard approximations; manufacturers vary slightly.
Frequently asked questions
How do I measure my ring size at home?
Two easy ways. (1) Measure a ring that already fits: use a millimeter ruler to measure the inside diameter, then enter it above. (2) Measure your finger: wrap a thin strip of paper or string around the base of your finger, mark where it overlaps, measure that length in millimeters, and enter it as the circumference. Measure at the end of the day when fingers are largest, and avoid measuring cold.
What is the difference between US, UK, and EU ring sizes?
They use different scales for the same finger. US/Canada sizes are numeric (e.g. 7). UK/Australia sizes are letters (e.g. N½). European (ISO 8653) sizes are simply the inside circumference in millimeters (e.g. 54). Japan uses its own numeric scale. This tool converts between all of them from a single measurement.
My size falls between two sizes — which should I pick?
Round up to the larger size, especially for wide bands, which fit more snugly. A ring that's slightly loose can be resized down or fitted with a sizer insert more easily than a too-tight ring can be stretched.
How accurate is an online ring size converter?
The conversions between standards are exact and industry-standard. The accuracy of your result depends on your measurement — a millimeter of error is about one full size. For an engagement ring or other important purchase, confirm with a jeweler or an inexpensive physical ring sizer before ordering.
Does finger size change?
Yes. Fingers swell in heat and after salty food, and shrink when cold. They can change with weight, pregnancy, and time of day. Measure a few times across different days and go with the largest reading for everyday comfort.