SuperDevTools
EN

Ring size chart and converter

Conversions use the formulas and charts most commonly published: from one jeweler or brand to another, a size can differ by half a size.

Convert a ring size

How to measure your ring size

  • Measure at the end of the day: fingers swell a little as the hours go by.
  • Avoid cold fingers (they shrink) and warm fingers after exercise (they swell).
  • The ring has to slide over the knuckle: if yours is large, measure around it too and keep the bigger number.
  • Between two sizes, go up, especially for a wide band.

1. With a ring that fits, placed on the screen

First, calibrate the screen: hold a payment card, or any ISO/IEC 7810 ID-1 card (85.60 × 53.98 mm, 3.370 × 2.125 in), against the screen and adjust the rectangle until it is exactly the same size.

Card 85.60 × 53.98 mm

Then lay your ring on the disc and adjust the disc until it fills the inside of the band exactly, without showing past it.

2. With a piece of string or a paper strip

  1. Wrap a thin string or a 5 mm (about 1/4 in) wide paper strip around the base of your finger, snug but not tight.
  2. Mark with a pen where the end meets the string, then check the loop slides over your knuckle.
  3. Unroll it, measure the length with a ruler and type it in below, in millimeters.

3. With a printable ring sizer

The PDF holds a 10 cm check line, two graduated strips to cut out (circumference in mm, US sizes and UK letters) and circles from 44 to 70 mm to lay a ring on.

Print at 100% (actual size), with "Fit to page" turned off, then measure the check line: it must be exactly 10 cm (3.94 in).

Ring size chart for every country

Columns shown

How the sizes are calculated

  • Reference: the finger circumference C in mm, which is the inside circumference of the ring. Inside diameter = C ÷ π.
  • France, Belgium, Germany (ISO 8653): the size is the circumference in mm (54 = 54 mm).
  • Germany, Netherlands: the size is the inside diameter in mm, in quarter millimeters (17.25).
  • Italy, Spain: size = circumference − 40, from 1 to 35 (54 mm = 14). Switzerland: same formula, in half sizes.
  • UK, Ireland, Australia: BS 6820 letters, 1.25 mm of circumference per letter, C = 40 mm (so A = 37.5 mm and N = 53.75 mm), half sizes, then Z+1 to Z+4.
  • US, Canada: diameter = 0.458 in + 0.032 in × size (11.63 mm + 0.8128 mm × size), about 2.55 mm of circumference per size.
  • Japan: No. 1 = 13 mm diameter, then 1/3 mm more per number (No. 14 = 17.33 mm).
  • Each size is converted to the nearest size, by circumference, in every other system.

Your size, settings and calibration are remembered on this device.

Find your ring size and convert it

In the US and Canada, ring sizes are numbers in half and quarter steps: each whole size adds 0.032 in (0.8128 mm) to the inside diameter. The UK, Ireland and Australia use letters, most of Europe uses the inside circumference in millimeters, Germany and the Netherlands use the diameter, and Italy, Spain and Switzerland subtract 40 from the circumference. This tool measures your finger three ways and shows the matching size in every system, which helps when you order a ring from abroad or read the size stamped inside a ring bought on a trip.

How to measure your ring size: three methods

  1. With a ring that fits. Under "1. With a ring that fits, placed on the screen", hold a payment card against the screen and adjust the rectangle to its size (3.370 × 2.125 in). Then lay the ring on the disc and move "Disc diameter" until the disc fills the inside of the band.
  2. With string or a paper strip. Wrap it around the base of your finger, mark where it meets, measure it with a ruler and type the result into "Measured length (mm)".
  3. With the printable ring sizer. Click "Download the ring sizer (PDF)", print at 100% with "Fit to page" turned off, then check with a ruler that the check line is exactly 10 cm (3.94 in). Wrap the strip around your finger, or lay a ring on the circles from 44 to 70 mm.

Measure at the end of the day, with fingers neither cold nor warm, and make sure the ring will slide over your knuckle.

Ring size chart: US, UK, Europe

Pick a system under "Convert from", then a "Size": the tool finds the nearest size in every other system and shows the difference in millimeters. The "Ring size chart for every country" can be filtered by circumference range and by column, then printed. Example: a US 7 measures 54.42 mm around (17.32 mm across), which is 54 in France, 14 in Italy and Spain, N½ in the UK and 14 in Japan. A US 6 measures 51.87 mm around, about 52 in Europe.

US, CanadaCircumference (mm)Diameter (mm)UK, AustraliaEurope (mm)
549.3115.70J49
651.8716.51L½52
754.4217.32N½54
856.9718.14P½57
1062.0819.76T½62

Wide bands, surprise rings and jeweler differences

Wide bands. A band wider than about 6 mm (1/4 in) covers more skin and feels tighter. Most people go up a quarter or half size, for example 7¼ or 7½ instead of 7.

Buying a surprise ring. Borrow a ring the person wears on the same finger for a few minutes and lay it on the on-screen disc or the printed circles. If you can't take it away, trace the inside of the band on paper with a sharp pencil and measure the diameter: 17 mm means 53.41 mm around, a US 6½. When unsure, size up slightly: making a ring bigger is usually easier than making it smaller.

Differences between jewelers. There is no single worldwide standard. The formulas here are the ones most often published (listed under "How the sizes are calculated"), but a jeweler's sizing can differ by half a size.

Frequently asked questions

What is the most common ring size?

For women, sizes 6 to 7 are the most frequent; for men, 9 to 10. These are only rough guides: always measure the finger the ring is for.

How do I convert a UK ring size to a US size?

Choose "UK, Ireland, Australia: letters", then the letter. UK N measures 53.75 mm around, which is a US 6½ in half sizes or 6¾ with "in quarter sizes".

Is the printable ring sizer accurate?

Yes, as long as it prints at the right scale: the check line must measure 10 cm. If it measures 9.7 cm, the printer shrank the page; turn off "Fit to page".

Are my measurements saved?

They stay in your browser on this device. Everything is calculated on your screen and nothing is sent anywhere.