Ring Size Finder

Step 1 of 2

Set the Scale

Lay the card down sideways, the long way, like the drawing below. Not upright.

The card sticks out on both sides

Resize the shape until the top and bottom edges match your card. Ignore the right side.

Lay your card like this

Adjust the wheel until this line measures 50 mm on your ruler.

Any card works: they are all exactly the same height.

Step 2 of 2

Take the Measurement

Place the ring on the disc and resize until the disc exactly fills the hole.

Leave a very fine line of background showing all the way round. That sliver is the room the ring needs to turn on your finger: close it completely and the ring will be too tight.

The hole
The whole ring
Your size 16
Inner diameter 17.8 mm
Show a specific size

Tap a size to see its exact diameter.

Wrap paper round the base of your finger and mark where it overlaps. Lay the strip along the ruler with its end on the 0, then move the line to your mark.

Your size 16
Diameter 17.8 mm

Measure at the end of the day, hands at normal temperature. If you have a ring that already fits, the ring method above is more reliable than paper.

Or print a paper sizer instead

More accurate: you read the size straight off the paper.

  1. Print the sheet at 100%. Turn off "fit to page" or "scale to fit".
  2. Check the printed square with a real ruler. It has to be exactly 50 mm on each side. If it is not, the print was scaled and the sizer will lie.
  3. Cut out the strip along the dashed line.
  4. Wrap it around the base of your finger, printed side out, snug but not tight.
  5. Read the number where the loose end crosses the start of the strip. That is your size.
Result

Your Size

CAS DEIÀ size 16

An estimate, not a jeweller's measurement. Between two sizes, take the larger.

SizeDiameterCircumference
It says a bigger size than the one I wear

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.

Why a bank card works

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.

Open This on Your Phone

The ring sizer measures against your screen, so it needs a phone you can lay a card and a ring flat on. Scan this code with your camera.

returns.casdeia.com/medidor

CAS DEIÀ — Paper Ring Sizer

Print this page at 100%, with "fit to page" or "scale to fit" turned OFF.

Measure this square first. 50 mm × 50 mm If it is not exact, print again at 100%.

Cut along the dashed line.

How to use it

1. Cut out the strip along the dashed line.
2. Wrap it around the base of the finger you will wear the ring on, printed side facing out. Snug, but loose enough to slide over the knuckle.
3. Hold the END marked START flat against your finger, so the 0 line is exactly where the loop begins.
4. With a pen, draw a line on the strip at the exact point where the loose end crosses over the START end. That pen mark is your measurement.
5. Unwrap the strip and read the number your pen line landed on. The bold number is your CAS DEIÀ size; the small number is the circumference in millimetres.
6. If your mark falls between two sizes, take the larger one. A ring that is too tight will not pass the knuckle.

Measure at the end of the day, hands at normal temperature. If you have a ring that already fits, the ring method above is more reliable than paper. If you can, measure three times and use the largest reading.