Ring Size Converter,
US, UK, EU and Japan.

Complete guide

How ring sizing works around the world.

Buying a ring online or as a gift for someone abroad is complicated by the fact that every major market uses a different sizing convention. A US size 7 is a UK N-and-a-half, an EU 54, and a Japanese size 14. None of those numbers look related, yet they all describe the same finger circumference. This guide explains each system so you can shop with confidence anywhere in the world.

The four major ring size systems

US and Canadian sizes

The US system uses whole and half numbers, typically ranging from size 3 (common for small women's fingers) up to size 13 or 14 for larger men's hands. The scale is based on the inner circumference of the ring, with each full size adding approximately 2.55 mm to the circumference (or about 0.81 mm to the diameter). Half sizes are common and recommended: a ring that is even slightly too tight is uncomfortable to wear and difficult to remove.

Canadian jewellers use the same numbering system as the US, so a US size 7 and a Canadian size 7 are identical.

UK, Australian, and New Zealand sizes

The British system uses letters, from A (smallest common size) up through Z and beyond (Z+1, Z+2, etc. for very large sizes). Half sizes use the fraction notation (for example, N½ falls between N and O). The UK system is also used in Australia, New Zealand, and Ireland.

Each full letter represents approximately 1.25 mm of inner circumference. Because the US system increments in larger steps (~2.55 mm per full size), one US size typically spans two UK letters. For example, US size 7 sits between UK N and O, usually listed as UK N½.

EU (ISO 8653) sizes

The European system is the most intuitive: the EU ring size is the inner circumference of the ring in millimetres, rounded to the nearest whole number. EU 54 is a ring with an inner circumference of 54 mm. Because it is directly tied to a physical measurement, EU sizes are gender-neutral and unambiguous. If you know your finger circumference in millimetres, you know your EU ring size. This is the system most commonly used in France, Germany, Spain, Italy, and the rest of continental Europe, as well as Russia and some Asian markets.

Japanese sizes

Japan uses a numerical system similar to the US but with different starting values and smaller increments. Japanese sizes typically run from about 1 to 30 for common adult sizes, with each integer step representing approximately 1.5 to 2.5 mm of circumference. The Japanese system is also used by some Korean and Taiwanese jewellers, though exact correspondences may vary slightly by brand.

How to measure your ring size accurately

The most reliable method uses a strip of paper and a ruler. Here is the step-by-step process:

1. Prepare your strip. Cut a narrow strip of paper about 15 cm (6 inches) long and less than 1 cm wide. Alternatively, use a piece of string.
2. Wrap it around the base of your finger. The base is where you will actually wear the ring. Make sure the paper wraps snugly but can still slide over the knuckle (the widest part of the finger). The ring must be able to go on and off.
3. Mark the overlap point. Use a pen to mark where the paper meets after one full wrap. This mark represents the circumference of your finger.
4. Measure the length. Lay the strip flat and measure from the end to your mark using a ruler. This length in millimetres is your finger circumference.
5. Enter the circumference into the calculator above and select "mm." The corresponding ring sizes in all four systems will appear instantly.

Common measurement mistakes to avoid

• Measuring at the wrong time of day. Fingers swell during the day, especially in warm weather or after exercise, and can shrink in cold temperatures. Measure in the evening and in a neutral temperature for the most representative reading.
• Pulling the paper too tight. The ring must be able to move over the knuckle. Wrap the paper comfortably rather than pressing it hard against the skin.
• Measuring the wrong finger. Fingers on your dominant hand are typically slightly larger. If you want to wear a ring on a specific finger, measure that finger exactly. Your ring finger on the left hand may be a different size from the ring finger on the right.
• Forgetting about band width. Wider bands tend to feel tighter than narrow bands of the same diameter. If buying a wide band (more than 6 mm), consider sizing up by half a size from your measured size.

What to do if you are between sizes

If your measurement falls between two standard sizes, the general rule is to round up to the larger size. A ring that is slightly loose is easier to resize and more comfortable to wear in warm weather than one that is slightly too tight. Extremely wide bands should always go up a half or full size for comfort.

Ring resizing after purchase

Most metal rings can be resized by a jeweller, typically by one to two sizes without significant structural change. Rings with stones set all the way around (eternity rings) are difficult or impossible to resize without removing and replacing stones. Rings made of alternative metals such as tungsten, titanium, and stainless steel generally cannot be resized at all. Always check the material and setting before purchasing if sizing is uncertain.

Disclaimer

This calculator uses lookup tables based on the GIA ring size guide and the Assay Office UK standard. Exact correspondences vary slightly between jewellers and countries. Always verify your size against the specific jeweller's chart before purchasing, especially for non-returnable or custom items.