How to measure your ring size at home

Best: measure a ring that already fits

A ring that fits the finger in question — same finger, same hand — is a measurement of the ring, not of a finger that changes size through the day. Put it on a ruler and read across the inside of the band, edge to edge, in millimetres. That is the inner diameter. Look it up in the diameter column of the chart: 16.5 mm is a US 6, 17.3 a US 7, 18.9 a US 9.

Read at the widest point of the inside, and read from directly above so the edges are not foreshortened. A ruler with millimetre marks is enough; a pair of callipers is better and costs little. If the band is not round — some are oval on the inside for comfort — measure the shortest way across and the longest, and average them.

Good: a strip of paper, or string

Cut a strip of paper about 5 mm wide, or use a length of thread. Wrap it around the base of the finger where the ring will sit — snug, so it does not slide, but not indenting the skin — and mark where it overlaps. Lay it flat and measure to the mark in millimetres. That is the circumference: the third column of the chart, and the EU size directly.

Do it three times and take the middle reading. Paper creases and string stretches, and a single reading is a guess dressed as a measurement. If the three disagree by more than a millimetre, the wrap is too loose or too tight; a millimetre of circumference is about a third of a US size.

• Paper 5 mm wide, or thread — not ribbon or elastic
• Around the base of the finger, snug not tight
• Three readings, take the middle
• The number is the circumference in mm: the EU size

Most certain: a ring sizer

A set of plastic or metal rings in every half size, from any jeweller or for a few pounds online. It is the only method that also tests the knuckle: a strip of paper can tell you the base of the finger is 54 mm around, but not whether a 54 will get past the joint. If the finger has a pronounced knuckle, this is the method to use, and the size to choose is the one that passes the knuckle with a little effort and does not spin at the base.

What puts people half a size out

Almost every wrong size comes from one of five things, and none of them is the ruler.

• Measuring in the morning or in the cold: fingers are smallest then. Measure at the end of the day, warm.
• Ignoring the knuckle: if it is larger than the base, the ring must pass it. Measure both, choose between.
• A wide band: 6 mm and up runs about half a size tight. Comfort-fit bands, rounded inside, fit nearer true.
• The other hand: the dominant hand is usually half a size larger. Measure the hand the ring is for.
• Rounding down: between sizes, go up. Loose can be fixed; too small cannot be worn.

Reading the result

Whichever method, you now have millimetres — a diameter or a circumference. Find it on the chart and read across for the US, UK or EU size, but when you order, give the millimetres too: charts disagree by half a UK letter because the systems do not line up, and a jeweller given 54.4 mm cannot misread it. The chart itself is on the ring size page, computed from the standards rather than copied.

Questions