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Ring Size Converter Calculator

Work out ring size converter instantly with clear inputs, formula shown and shareable results.

About Ring Size Converter Calculator

Ring sizing is fundamentally a circumference measurement: EU sizes are the circumference in millimetres directly, while US sizes run in steps of about 0.8 mm of circumference from a 36.5 mm base at size 3.5. A 17.3 mm inner diameter is 54.3 mm around, roughly a US 7 or a UK N.

Formulas

Circumference

C = pi x inner diameter

US size

size = (C - 36.5) / 2.55 + 3.5, approximately

Worked example

With the default values below, Ring Size Converter Calculator returns US Ring Size of 10.5. Change any input above and every figure here is recalculated in your browser.

Inputs used

Ring inner diameterminimum 5 mm
17.3 mm
Show size inone of UK and Australia (letters), US and Canada (numbers), EU (circumference)
UK and Australia (letters)

Results

US Ring Size
10.5
Inner Circumference
54.35 mm
Approximate UK Letter Size
Q
EU Size (Circumference In mm)
54.4

Step by step

  1. 1Values used
  2. 2Circumference
  3. 3US size
  4. 4US Ring Size= 10.5
  5. 5Inner Circumference= 54.35 mm
  6. 6Approximate UK Letter Size= Q
  7. 7EU Size (Circumference In mm)= 54.4

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How do I measure my ring size at home?

Measure the inner diameter of a ring that fits, or wrap a strip of paper around the finger and measure its length as circumference.

Does finger size change?

Yes - by up to half a size with temperature, time of day and salt intake. Measure warm and at the end of the day.

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