Find your ring size by diameter or circumference, or convert between US, UK and EU sizing systems.
What Is Ring Size Calculator?
Ring sizing uses different systems depending on the country — the UK uses letters (H, J, L, N), the US uses numbers (5, 6, 7, 8) and Europe uses the inner circumference in millimetres (48, 50, 52). Converting between these systems is essential when buying rings from international jewellers or ordering engagement rings from overseas.
The most accurate way to determine ring size is by measuring the inner diameter or circumference of a ring that fits well. This calculator converts between UK, US and EU sizing and provides the corresponding millimetre measurements for precise fitting — free, with no sign-up required. Premium adds the full size chart at a glance and a printable, true-to-size ring sizer you can cut out and wear.
How to Use This Tool
Enter your known ring size in any system (UK letter, US number, EU mm).
View the equivalent sizes in the other systems.
Or enter the inner diameter or circumference in millimetres for an exact match.
Use the measurement guide to measure an existing ring that fits well.
Premium: print the ring sizer strip at 100% scale, cut it out, and wrap it around your finger to read your size directly.
Tips & Best Practices
Measure an existing ring that fits the correct finger — using a ring that fits a different finger will give the wrong size.
Fingers change size throughout the day and with temperature — measure at room temperature in the evening.
For surprise engagement rings, try measuring a ring the recipient already wears on that finger.
Half sizes exist in most systems — if you are between sizes, go up rather than down.
Common Use Cases
Converting ring sizes when ordering from international jewellers.
Determining the correct size for an engagement ring or wedding band.
Converting between UK letter sizes and US/EU numeric sizes.
Finding your ring size from a millimetre measurement.
Frequently Asked Questions
How do I measure my ring size?
Measure the inner diameter of a ring that fits, or wrap string around your finger and measure the circumference in millimetres.