Ring Size Converter

How to Measure Ring Size With String or Paper

The string method is the oldest home sizing trick and still the most useful. All you need is string or paper, a pen and a ruler with millimetres.

Quick answer

Wrap, mark, measure in millimetres, divide by 3.14 for the diameter, then look the number up. A 54 mm string reading is a US 7 / UK N½.

Instant Converter

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Inside circumference, mm

Inside

Inside

Inside

Inside

Matched inside diameter 17.30 mm · circumference 54.35 mm

Steps

  1. Step 1: Cut a strip

    Cut a strip of paper about 5 mm wide, or use a piece of non-stretchy string.

  2. Step 2: Wrap it

    Wrap it around the base of the finger — snug, but not tight enough to dent the skin.

  3. Step 3: Mark the overlap

    Mark the point where the end meets the strip with a fine pen.

  4. Step 4: Measure flat

    Unwrap it, lay it against a ruler, and read the length in millimetres.

  5. Step 5: Convert

    Divide by 3.14 for the inside diameter, or use the circumference directly in the converter.

Why string can read small

  • Elastic string stretches and gives a reading up to a full size small — use paper or cotton thread.
  • Pulling tight compresses the skin. Wrap so the strip can just rotate.
  • Cold fingers shrink. Warm your hands first.
  • Forgetting the knuckle: check that a loop of that size would slide over it.

Paper strip vs string

Paper is easier to mark accurately and does not stretch, so it is the better choice. String is more comfortable around a swollen or arthritic knuckle because it conforms to the shape.

Double-check your result

Repeat the measurement three times and average the readings. If the results vary by more than 1 mm, your wrap tension is inconsistent — try the paper strip instead, or print a sizing chart and compare an existing ring.

Frequently asked questions

What do I divide my string measurement by?

Divide by 3.14159 (π) to convert the circumference into the inside diameter in millimetres.

Can I use dental floss?

It works but it is thin enough to cut into the skin and read small. A 5 mm paper strip is more accurate.

Keep reading

For an expensive ring, confirm the size with a jeweller before ordering — see the ring size FAQs for resizing advice.