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Ring Size Converter
Convert a ring size between US and Canadian numbers, UK and Australian letters, EU sizes and Japanese numbers — or find the size from a ring’s inside diameter or the circumference of your finger in millimeters.
- US / Canada
- 7
- UK / Australia
- N½
- EU size (inside circumference)
- 54.4 mm
- Inside diameter
- 17.32 mm
- Japan
- 14
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Choose what you know: a size in one system, or a measurement.
- Enter the size, or the UK letter.
- Read the equivalents in the other systems.
- Confirm with a jeweler’s ring gauge before ordering an expensive ring.
Worked examples
A US size 7 ring
- Inside diameter
- 17.32 mm
- EU size (inside circumference)
- 54.4 mm
- UK / Australia
- N½
- Japan
- 14
- Ring sizes
- US 7 · UK N½ · EU 54.4 · 17.32 mm
A finger that measures 60 mm around
- Inside diameter
- 19.1 mm
- US / Canada
- 9.25
- UK / Australia
- S
- Japan
- 19
A UK size L ring
- EU size (inside circumference)
- 51.3 mm
- Inside diameter
- 16.31 mm
- US / Canada
- 5.75
- Japan
- 11
How the systems are defined
US and Canadian sizes step by 0.032 inch (0.8128 mm) of inside diameter per full size, so a size 7 is 17.32 mm across. European sizes under ISO 8653 are simply the inside circumference in millimeters — a 54 fits a 54 mm finger. UK and Australian sizes use letters, each about 1.25 mm of circumference apart, with half sizes in between. Japanese sizes step by a third of a millimeter of diameter.
Because each system has different step sizes, conversions land between sizes and are rounded to the nearest quarter size (US), half letter (UK) or whole number (Japan). Published charts from different jewelers can disagree by a quarter to half a size.
Measuring at home
The most reliable way is to measure the inside diameter of a ring that already fits the same finger. Alternatively, wrap a strip of paper around the base of the finger, mark where it overlaps and measure the length in millimeters — that is the circumference. Make sure it slides over the knuckle.
Fingers swell when warm and at the end of the day and shrink when cold, so measure at room temperature in the afternoon or evening. Wide bands fit tighter: for a band over about 6 mm wide, most jewelers suggest going up a quarter to half a size.
Questions people ask
What is a US size 7 ring in mm?
17.32 mm inside diameter and 54.4 mm inside circumference, which is an EU size 54–55 and a UK N½.
What is a US size 6 ring in UK size?
UK L½. A US 6 has an inside diameter of 16.51 mm and a circumference of 51.9 mm.
How do I measure my ring size with string or paper?
Wrap it snugly around the base of the finger, mark the overlap and measure the length in millimeters. Enter that as the circumference. A 60 mm finger is about a US size 9¼.
Are EU ring sizes the circumference?
Yes. The ISO standard used across most of Europe defines the size as the inside circumference in millimeters.