Ring Size Converter
Ring sizing systems vary widely by country: the United States and Canada use a numeric scale starting around 3, the United Kingdom and Australia use letters from F to Z, continental Europe uses a numeric scale based on the inner circumference in millimetres, and the inner diameter (mm) provides a universal physical measurement. Converting between these systems is essential when buying or gifting jewellery internationally.
This converter uses a standard industry lookup table to map each US size to its UK, EU, and inner-diameter equivalents. When you enter a diameter value, the tool finds the closest matching standard size to within the nearest increment. Always verify with the jeweller if you are between sizes, as different brands may use slightly different sizing conventions.
How it works
Conversions are based on a standard lookup table derived from ISO 8653 and industry-standard ring sizing charts. EU size equals the inner circumference in mm rounded to the nearest whole number; inner diameter (mm) = EU size / π. For diameter input the nearest table entry within ±1 mm is returned.
Use cases
- Converting a US ring size to EU when buying online from a European jeweller
- Finding the UK equivalent of a ring received as a gift from abroad
- Measuring your finger diameter with a ruler and converting to US or EU size
- Resizing or ordering a custom ring from an international manufacturer
- Comparing ring sizes across different country standards when travelling
Frequently asked questions
How do I measure my ring size at home?
Take a ring that fits the intended finger well and measure its inner diameter in millimetres with a ruler, then enter that value in the converter to find the closest US, UK, and EU sizes. Alternatively, wrap a strip of paper snugly around the finger, mark where it overlaps, and measure the length in mm — that circumference is directly the EU size. Measure at the end of the day, when fingers are slightly larger.
How do EU ring sizes work?
The continental European system simply uses the inner circumference of the ring in millimetres, rounded to the nearest whole number, following ISO 8653. That means an EU 54 ring has a 54 mm inner circumference and an inner diameter of 54 ÷ π ≈ 17.2 mm. It is the most direct system because the size is itself a physical measurement.
What is a US ring size 7 in EU?
A US size 7 corresponds to approximately EU 54, with an inner diameter of about 17.3 mm. In the UK lettering system it falls around N½–O, since charts from different jewellers can differ by half a size. This converter uses a standard industry lookup table to map all four values at once.
What should I do if I am between two ring sizes?
Most jewellers recommend choosing the larger of the two sizes, especially for wider bands, which fit more snugly than thin ones. Keep in mind that different brands may use slightly different sizing conventions, so confirm the exact measurement with the jeweller before buying. Finger size also varies with temperature and time of day.
Are ring sizes the same in every country?
No. The US and Canada use a numeric scale starting around 3, the UK and Australia use letters from F to Z, and continental Europe uses the inner circumference in millimetres. Because these scales are unrelated, converting between them requires a lookup table — or the universal fallback of measuring the inner diameter in mm, which this tool accepts directly.