Skip to content
SizeCheck
EN

Ring size converter: inches, cm and mm to ring size

Turn a measurement in inches, cm or mm into your ring size, or convert a size you already know between countries. Uses the published formula for each system.

Runs in your browser. Nothing is uploaded.

I have a measurement

I know my size in one country

Inches to ring size chart

Measured around your finger with a string or paper strip? Find the length here. Values are circumference, in sixteenths of an inch as a tape measure shows them.

Around finger (in)Decimal inmmUSUKEU
1 3/4" 1.750 44.4 3 F½ 44
1 13/16" 1.813 46.0 3¾ H 46
1 7/8" 1.875 47.6 4¼ I 48
1 15/16" 1.938 49.2 5 J½ 49
2" 2.000 50.8 5½ K½ 51
2 1/16" 2.063 52.4 6¼ M 52
2 1/8" 2.125 54.0 6¾ N 54
2 3/16" 2.188 55.6 7½ O½ 56
2 1/4" 2.250 57.1 8 P½ 57
2 5/16" 2.313 58.7 8¾ R 59
2 3/8" 2.375 60.3 9¼ S½ 60
2 7/16" 2.438 61.9 10 T½ 62
2 1/2" 2.500 63.5 10½ V 64
2 9/16" 2.563 65.1 11¼ W 65
2 5/8" 2.625 66.7 11¾ X½ 67
2 11/16" 2.688 68.3 12½ Y½ 68
2 3/4" 2.750 69.8 13 Z+1 70
2 13/16" 2.813 71.4 13¾ Z+2 71
2 7/8" 2.875 73.0 14¼ Z+3½ 73
2 15/16" 2.938 74.6 15 Z+4½ 75
3" 3.000 76.2 15½ Z+6 76

How to measure for the converter

  1. Cut a thin strip of paper, about 5 mm (1/4 in) wide. String works too but stretches, so paper is better.
  2. Wrap it around the base of the finger, snug but able to slide over the knuckle.
  3. Mark where the end overlaps, unwrap it, and measure from the end to the mark with a ruler.
  4. Enter that length above as circumference. Do it three times and use the middle result.

Have a ring that fits? Measure straight across the inside, edge to edge, and enter it as diameter. Or skip the ruler and use the on-screen ring sizer.

The formulas behind each system

  • US & Canada: inside diameter = 0.458 in + 0.032 in × size (11.63 mm + 0.8128 mm × size).
  • UK & Australia: letters A to Z, then Z+1 and up. Each letter is 1.25 mm of circumference; C is 40 mm (BS 6820).
  • EU / ISO 8653: the size is the inside circumference in mm. Used in France, Belgium, Austria and the Nordic countries.
  • Germany: shops use the inside circumference in mm, the same as EU sizes. Some charts list the inside diameter in mm instead, so check which one a shop means.
  • Italy, Spain, Switzerland, Brazil & Portugal: circumference in mm minus 40. ISO 54 is size 14.
  • Japan & China: size 1 is 13.0 mm across, and each size adds 1/3 mm of diameter.

The full side-by-side table is on the ring size chart page.

Common questions

How do I convert inches to ring size?
Wrap a thin strip of paper or string around the base of your finger, mark where it overlaps, and measure that length in inches. That is the circumference. Enter it above, or find it in the inches table: 2 1/8 inches is about a US 7, and every extra 1/10 inch is about one size up.
What is the formula for US ring size?
US size = (inside diameter in inches − 0.458) ÷ 0.032. In millimetres: size = (diameter − 11.63) ÷ 0.8128, or from circumference: size = (circumference − 36.5) ÷ 2.55. Each whole size is 0.032 inch (0.81 mm) of diameter.
Circumference or diameter: which should I enter?
Circumference if you measured around your finger with a strip or string. Diameter if you measured straight across the inside of a ring that fits. Diameter is about 3.14 times smaller, so mixing them up gives a nonsense size. The converter warns you if a value looks like the wrong one.
How do I convert cm to ring size?
Set the unit to cm and enter the circumference. 5.4 cm around is about a US 7, UK N, EU 54. EU sizes are simply the circumference in millimetres, so 5.4 cm = 54 mm = EU 54.
Why do some charts give slightly different sizes?
US sizes come from an old inch scale, UK letters from a British Standard, and EU sizes from ISO 8653 millimetres. They do not line up exactly, so every conversion is rounded to the nearest size a shop sells. UK charts from different jewellers also vary by up to half a size. This converter uses the published formulas for each system.

Next