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Ring size calculator

Measure the inside diameter of a ring or the circumference of your finger and get your ring size in US, UK, EU and Japanese systems, with nearby sizes and fitting tips.

13 mm26 mm

The blue line is the inside edge of your ring, the hole the finger goes through; the grey band stands for the metal around it. Lay a ring that fits on the screen so the blue circle shows through the hole, then move the slider until the blue line just touches the inside of the ring.

Result does not match a ring that fits? Fine-tune the scale with a coin

Pick a coin you have. Press Place coin: touches on the outline are ignored for 15 seconds so the coin does not move the page. Lay the coin flat on the outline, then use the buttons until the outline matches the coin edge exactly.

coin
Scale: 3.78 px/mm
What did you measure?
Units
mm

Type it, or use the slider under the ring.

Your size in each system

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Nearby sizes

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DiameterUSUKEUJapan

Getting the fit right

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Ring sizes are just a measurement in disguise: the inside diameter or circumference of the ring. Every country wraps that number in its own scale, US numbers, UK letters, EU millimetres of circumference, so converting between them needs a table. This calculator takes the raw measurement and returns the size in each system.

How to measure

  • On screen: calibrate once with a bank card, then lay a ring that fits on the circle and move the slider until the ring’s inside edge lines up. This is the quickest method and accurate to about a quarter size.
  • From a ring that fits: measure the inside diameter with a ruler or calipers, edge to edge through the centre. This is the most accurate method.
  • From your finger: wrap a strip of paper or string snugly around the base of the finger, mark where it overlaps, and measure the length. That is the circumference. Do it in the evening, when fingers are largest.

How it is calculated

  1. Circumference is converted to diameter (÷ π) if that is what you measured; inches are converted to millimetres.
  2. The diameter is matched to the nearest standard size. US sizes step by about 0.4 mm of diameter per half size; EU sizes are the circumference in millimetres.
  3. If your measurement falls between two sizes, the note under the result says which way to round.

Example

A ring with an inside diameter of 17.3 mm is US 7, UK N½, EU 54.5, Japan 14. The finger circumference would be about 54.4 mm (2.14 in).

Common mistakes

Measuring in the morning or in the cold gives a size too small. Using a wide string that does not lie flat gives a size too large. Wide bands (over 6 mm) feel tighter than thin ones at the same size. When buying as a surprise, borrowing a ring the person wears on the same finger is the reliable trick; fingers on the two hands can differ by half a size.

Frequently asked questions

How do I find my ring size at home?

Measure the inside diameter of a ring that fits, or wrap string around the base of your finger and measure it. Enter the number above and read the size in your country’s system.

What is the average ring size?

About US 6–7 (UK L–N) for women and US 9–10 (UK S–T) for men, but the spread is wide. Average is a poor substitute for measuring.

How do I convert US ring size to UK or EU?

Through the diameter: each US size is a fixed inside diameter, and the table maps it to the UK letter and the EU circumference. US 7 is UK N½ and EU 54.5.

Should I size up for a wide band?

Usually half a size for bands wider than 6 mm, because more metal in contact with the finger feels tighter.

Can rings be resized?

Most plain gold, silver and platinum rings can be resized up or down by one or two sizes. Eternity bands, tungsten, titanium and rings with stones all the way round usually cannot.

Sources

  1. ISO 8653: Jewellery — Ring-sizes — Definition, measurement and designation
  2. Ring size conversion (Wikipedia, with national standard references)

By Calcelate Team. Formula from the sources above.

  1. 2026-09-14 · Formula and texts checked
  2. 2026-09-14 · Reference data as of this date