Ring Size Converter

How to Use the Ring Size Converter

Our ring size converter helps you find the perfect ring size by converting measurements between millimeters, centimeters, and inches. Enter the inner diameter or inner circumference of a ring, and instantly see equivalent sizes for US, UK, EU/ISO, France, Germany, Switzerland, and Japan/China sizing standards. Whether you are shopping for an engagement ring, a wedding band, or a fashion ring, this tool ensures you get the right fit every time.

Ring sizing varies across countries and regions. The US and Canada use a numerical scale with half sizes, while the UK and Australia use alphabetical designations. European countries like France, Germany, and Switzerland have their own numbering systems, and Japan follows a different numerical scale. Our converter handles all these standards simultaneously so you never have to consult multiple charts.

Ring Diameter vs. Ring Circumference

The two key measurements for ring sizing are the inner diameter and the inner circumference. The inner diameter is the straight-line distance across the center of the ring from one inner edge to the other. The inner circumference is the total length around the inside of the ring. These measurements are related through the mathematical constant pi (π):

$$Circumference = Diameter \times \pi$$

$$Diameter = \frac{Circumference}{\pi}$$

For example, if your ring has an inner diameter of 16.5 mm, the inner circumference is approximately 51.8 mm. If you measure the circumference at 60 mm, the inner diameter is about 19.1 mm. Our tool handles these conversions automatically so you can input whichever measurement is most convenient.

How to Measure Your Ring Size at Home

If you do not know your ring size, you can measure it at home using a few simple methods:

Method 1: Measure an Existing Ring

Take a ring that fits the intended finger well. Using a ruler, measure the inner diameter in millimeters from one inner edge to the opposite inner edge. For the most accurate result, measure across the center of the ring. You can also measure the inner circumference using a piece of string placed along the inside edge.

Method 2: Use a String or Paper Strip

Wrap a piece of string or a strip of paper around the base of the finger where the ring will sit. Mark where the ends meet. Measure the length in millimeters using a ruler. This gives you the finger circumference. Enter this measurement into the tool selecting circumference as your measurement type to find your ring size.

International Ring Size Standards

Different regions of the world use different ring sizing systems. Here is a quick overview of the major standards:

• US & Canada: Numerical scale from 0 to 15 with half-size increments. Size 7 is the average for women and size 10 is the average for men.
• UK & Australia: Alphabetical scale from A to Z with half-letter increments. Size M is a common average.
• EU / ISO: The size number equals the inner circumference in millimeters. For example, EU 54 means approximately 54 mm inner circumference.
• France: Similar to the EU system — the size closely matches the inner circumference in millimeters.
• Germany: Numerical scale based on the inner diameter in millimeters. For example, German size 17 corresponds to roughly 17 mm inner diameter.
• Switzerland: Similar to Germany but with slightly different numbering.
• Japan & China: Numerical scale (typically 1–30) based on inner circumference, similar to but not identical with US numbering.

Our ring size converter handles all these standards so you can find the right size no matter which country's sizing system you need.

Tips for Accurate Ring Sizing

For the most accurate ring size measurement, consider these helpful tips:

• Measure your finger at the end of the day when it is at its largest.
• Avoid measuring when your hands are cold, as fingers can be up to half a size smaller.
• Measure the specific finger as ring sizes can vary between different fingers on the same hand.
• Consider the ring width: wider bands may need a slightly larger size for comfortable fit.
• If between sizes, choose the larger size for comfort, especially for rings worn daily.
• Have your size measured by a professional jeweler for the most reliable result.