Measure Ring Size

Method

Measure ring size with string

String is the method everyone has heard of and the one most likely to mislead: it works, but only if you pick the right string, mark it carefully, and accept that it reads a little large. Use it when you have nothing else — and know its bias.

Why string is the weakest finger method

String stretches

Almost every household string — sewing thread, yarn, twine — lengthens when pulled. A string pulled snug around a finger and then laid flat relaxed is longer than the finger's circumference was. That makes the size read large, often by a full half-size.

The mark is the measurement

With tape you read a number directly. With string you make a pen mark, then measure from the end to the mark with a ruler — two chances to be off by a millimetre, and the mark itself has a width. A thick pen mark is a 1 mm error before you start.

It is still better than guessing

None of that makes string useless. A careful string measurement, repeated and read honestly, gets you within a size of the truth — which is enough to order a resizable ring, and far better than borrowing another finger's size.

Step by step, with the stretch controlled

  1. Pick the least stretchy string you have

    Non-stretch thread, dental floss (unwaxed, unflavoured is fine), or a thin strip of paper is better than yarn or elastic. Do not use elastic, ribbon, or anything that springs back — those do not measure, they guess.

  2. Wrap once, snugly, at the base

    Wrap around the base of the exact finger, in the evening, finger straight and relaxed. Mark the point where the string meets itself with a fine pen — one thin line, not a blob.

  3. Do not pull the string taut to measure it

    Lay the string flat on a table next to a ruler, with no tension on it at all, and read from the end to the mark in millimetres. Pulling it straight stretches it again and adds the very error you are trying to avoid.

  4. Repeat three times and take the middle value

    String readings scatter. Three wraps, three marks, three ruler readings: discard the highest and lowest if they disagree, and keep the middle one. If all three disagree by more than 2 mm, the string is too stretchy — switch to a paper strip.

  5. Convert, and round down a touch

    Type the circumference into the calculator below. Because string bias runs large, if your result sits exactly between two sizes, prefer the smaller one — the opposite of the usual between-sizes advice, and only for string measurements.

Convert your string measurement

Decimal numbers are welcome. Use a dot for decimals, for example 16.5.

What you measured

Circumference

Changing the unit reinterprets the number you typed in the new unit — it does not convert it. Re-enter the number if you measured in a different unit.

Note: Tension: snug, not tight — the strip should slide over the knuckle with slight resistance, and should not dent the finger. Knuckle: if your knuckle is wider than the finger base, size for the knuckle, or the ring will not go on. Measure in the evening, with warm hands, and repeat twice, taking the largest reading.

Try an example

Highlight my country's size

Enter a measurement to see your size.

Formulas: circumference = π × diameter; diameter = circumference ÷ π. Matching uses your full, unrounded value; displayed diameter is rounded to 2 decimal places and circumference to 1 decimal place.
Warning: If you can get a flexible tape or a paper strip, use that instead — both skip the stretch problem entirely. The tape page and the finger page explain those methods, and they rank above string for a reason.

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