Find your ring size at home, with a bank card and thirty seconds.
Lay any card (credit, debit, ID) flat on the shape below. Resize it until the top and bottom edges line up with your card. Ignore the right side, the shape runs off the screen on purpose.
Use the buttons for fine tuning. Every bank card in the world is the same height, which is what makes this work.
Place a 1 € coin on the circle. It should match exactly. If it does not, your card was not lined up properly and everything you measure next will be wrong.
This circle is 23.25 mm, the exact diameter of a 1 € coin.
Place the ring on the disc and resize until the disc is just covered: no colour showing underneath the band, and no gap inside it.
Tap a size and the disc jumps to its exact diameter. Useful for checking against a ring whose size you already know.
Wrap a thin strip of paper around the base of your finger, snug but not tight, and mark where it overlaps. Straighten the strip and lay it along the ruler, with the end at the first line.
Measure late in the day and never with cold hands. Fingers change size as the day goes on.
A printed strip is more accurate than eyeballing a screen, because you read the size straight off the paper wrapped around your finger.
This is an estimate, not a jeweller's measurement. If you fall between two sizes, take the larger one: a ring that is too tight will not pass the knuckle.
| Size | Diameter | Circumference |
|---|
Almost always this means the ring was measured on the outside. What counts is the inner hole: a size 20 ring is 19.10 mm across on the inside but around 21 mm on the outside, and that gap is two full sizes. This is why the circle is solid, the ring has to cover it completely.
Every card in the world is made to the ISO 7810 ID-1 standard: 85.60 × 53.98 mm, no exceptions. By matching the shape to your card, this page learns how many pixels make a millimetre on your particular screen, and from there it can draw at true size.
Print this page at 100%, with "fit to page" or "scale to fit" turned OFF.
Cut along the dashed line.
How to use it
1. Cut out the strip.
2. Wrap it around the base of your finger, printed side facing out, snug but not tight.
3. Line up the END marked START with the edge of the loop.
4. Read the number where the loose end crosses the start. The bold number is your CAS DEIÀ size; the small number is the circumference in millimetres.
5. If you land between two sizes, take the larger one.
Measure late in the day and never with cold hands. Fingers change size as the day goes on.