Jewelry sizing

Ring Size Calculator

Measure the inside diameter of a ring that fits, or wrap a strip of paper around your finger to get the circumference. Enter it in millimeters, or pick a size you already know, to see it in every system.

—US / Canada
—UK / Australia
—EU / ISO
—Swiss
—Diameter (mm)
—Circumference (mm)
USUKEU / ISOSwissDiameter (mm)Circumference (mm)

Calculated on your device. Nothing is uploaded to a server.

How to use the ring size calculator

  1. MeasureMeasure a ring that fits across its inside, or wrap paper around the base of your finger and mark where it overlaps.
  2. Enter the valueChoose diameter or circumference and type the millimeters, or pick a size you know.
  3. Read your sizesSee the US, UK, EU and Swiss sizes, highlighted on the chart.

How ring sizes are calculated

A ring size is a measure of the inside of the band. In the US and Canada, sizes follow a linear scale where each full size adds about 0.8128 mm to the inside diameter, starting from about 11.63 mm at size 0. So a US 7 is about 17.3 mm across and 54.4 mm around. The UK and Australia use letters, each about 1.25 mm apart in circumference, with half sizes in between. Most of Europe uses the ISO system, where the size is simply the inside circumference in millimeters. Swiss sizes are that circumference minus 40. Use the chart as a guide. Wide bands usually need about half a size larger.

Measure at the right time

Fingers are smaller when cold and larger in the evening or in hot weather. Measure at room temperature in the afternoon.

Knuckle check

If your knuckle is much wider than the base of your finger, choose a size between the two measurements so the ring slides on but doesn't spin.

Ring Size Calculator FAQ

How do I measure ring size at home?

Wrap a thin strip of paper around the base of your finger, mark where it meets, and measure the length in mm. That's the circumference.

What is the most common ring size?

For women, US 6 to 7 is most common. For men, it's US 9 to 10.

What is the EU ring size?

The EU/ISO size is the inside circumference in millimeters. A size 54 ring is 54 mm around the inside.

How do UK letter sizes compare to US sizes?

Roughly, US 5 is J½, US 7 is N½ and US 9 is R½. The chart shows the full conversion.

Should I size up for a wide band?

Yes. Bands wider than about 6 mm usually feel tighter, so many jewelers recommend going up a quarter to half a size.

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