Ring Size Conversion Charts

Most ring size systems are based on whole sizes, and some also include half sizes, like the US and UK systems. However, some jewelers, especially those who create custom pieces, work with even finer increments such as quarter or eighth sizes. This allows for a more precise fit, which is particularly helpful for engagement rings or fine jewelry where accuracy matters.

These fractional sizes still follow the logic of the main system. For example, in the US system, each full size adds about 0.032 inches in inner diameter, so a quarter size adds roughly 0.008 inches.

You can find these quarter sizes in our complete ring size chart under the US size column.

This traditional sizing method is used in countries such as Switzerland, France, Italy, and Spain. Although it’s the same system, people refer to it differently depending on the country. Ring sizes are calculated by subtracting 40 from the ring’s inner circumference in millimeters. For example, a ring with a 54 mm circumference is labeled as size 14.

These countries now officially follow the ISO-based European system, where the size matches the inner circumference. Still, the “minus 40” method is widely used in practice.

On this site, we refer to it as the “French system” for clarity, as France is strongly associated with its early and continued use.

Yes, you can reliably convert ring sizes between systems using detailed conversion tables, especially when they are based on exact diameter or circumference values. However, many simplified tables use rounded numbers to make them easier to read. This can lead to small differences when switching between systems.

For the most accurate results, measure the inner diameter or circumference of your ring or finger, and use a complete conversion chart like the one on this site, which includes exact values for each size.

Each ring size system follows its own scale and increments, so it’s normal for a size in one system to fall between two options in another. For instance, a diameter of 19.7 mm corresponds to size 62 in the EU system, T½ in the UK system, and falls between US sizes 9.5 and 10.

When this happens, the best approach is to choose the closest equivalent in the target system using our complete ring size conversion chart.

Some countries have official standards that regulate how ring sizes are measured and designated, while others rely on widely accepted but unregulated systems.

The main national and international standards include:

• ISO 8653:2016 sets the global reference. It uses the inner circumference in millimeters, measured with a calibrated ring stick (±0.02 mm tolerance). Sizes range from 41 to 76.
• JIS S 4700:2022 is the Japanese version, based on ISO but adapted to use inner diameter (in mm). It supports fractional sizes and defines ranges from 13 to 24.33 mm in diameter.
• BS EN 28653:1993 is the British adaptation of ISO 8653, used as a metric basis behind the UK’s alphabetical sizing.
• NBR 16058:2012 is the Brazilian standard. It also derives from ISO but uses the formula T = (D × π) – 40, based on the inner diameter (D) in mm.

Japan uses a standardized system defined by JIS S 4700:2022, where ring sizes are based on the inner diameter in millimeters, increasing in consistent 0.33 mm steps. This system is officially used in Japan and often referenced in other parts of Asia.

In countries like China, South Korea or Hong Kong, local sizing systems are also commonly used. They usually follow numeric scales and use diameter increments around 3 mm, although these are less precise than in standardized systems. Each country applies its own conventions and numbering, without official regulation.

Because of these similarities, some charts group them together under the Japanese or Asian system, while others list them separately to reflect differences in how the sizes are labeled or calculated.

To avoid confusion, the best approach is to measure the ring’s inner diameter and use the specific conversion chart provided by the manufacturer or retailer, especially when dealing with regional or non-standard systems.