Printable ring sizer

Print the ring sizer at Actual size and check it with a bank card first. Then either lay a ring that fits on the circles — the right size is the circle whose line sits just inside the ring all the way round — or cut out the strip, wrap it round the base of the finger and read the size where the START line meets the scale. With string or a strip of paper, mark where it overlaps, measure that length with a ruler and enter it above.

Because a printer that shrinks the page makes every size read too large, and the shrink is too small to spot by eye. The usual Fit to page setting prints at about 97%; on that page a finger that is a US 7 reads about 7.7. Bank, credit and ID cards are all made to one size, 85.60 × 53.98 mm, so a card that exactly covers the box proves the page printed true.

Take the larger one. Fingers are bigger at the end of the day and in warm weather, and a ring has to pass the knuckle. For a wide band — roughly 6 mm or more — many jewellers suggest going up a quarter to a half size, because a wide band sits tighter than a narrow one of the same size.

They measure the same thing in different ways. European sizes (ISO 8653) are the inside circumference in millimetres. US sizes add 0.032 in (0.81 mm) of inside diameter per size, from 0.458 in at size 0. UK and Australian sizes are letters, 1.25 mm of circumference apart, from 37.5 mm at A. Japanese sizes add a third of a millimetre of diameter per size from 13 mm at size 1. The chart above converts between them through the circumference.

For a ring you already own, laid on the circles, yes — to about a quarter of a US size once the card check passes. Paper strips are less reliable, because paper does not bend like a metal band and it is easy to pull a strip too tight or leave it loose; measure two or three times. For an expensive ring, a jeweller’s ring gauge is still the reference.