Ring Size Converter

Ring sizes are written completely differently around the world: the United States and Canada count in numbers with quarter steps, the United Kingdom, Ireland and Australia use letters from A to Z, continental Europe and the ISO 8653 standard use the inner circumference in millimetres, and Japan has its own numeric scale. This converter translates any of them into any other in one step.

Pick the system you know, pick the system you need, and enter the size — a number for US, EU or Japanese sizes, a letter such as M or M½ for UK sizes, or a raw measurement in millimetres. Besides the converted value, the tool shows the closest standard row across every system at once, including the inner diameter and circumference, so you can double-check the match before ordering.

If you do not know any size yet, the built-in instructions explain the two reliable ways to measure at home: wrap a thin strip of paper or thread around the base of your finger and measure the length, or measure the inner diameter of a ring that already fits well. Millimetre inputs are linearly interpolated between the table rows, so even an in-between measurement lands on the nearest realistic size.

Everything runs locally in your browser — no sign-up and no data sent anywhere. Note that UK and Japanese equivalents are the closest published matches rather than exact algebra: jewellers' charts can differ by up to half a step, so when a ring sits between two sizes, choose the larger one.