No camera needed
Ring Sizer
Step 1 / Calibrate
Turn the card upright. Adjust the blue lines.
Turn your credit/debit card upright (portrait).
Place it flat, then match its 53.98 mm short edge between the blue lines.
53.98 mm
Use a rigid, round ring that already fits this finger.
Adjust the blue circle until its inner edge matches the inner edge of your ring. A similar band width gives the best result.
Inner edge
Place finger here
Light touch - no pressure
COLMI size
Size 8
Inner diameter
18.1 mm
Starting width is estimated. Confirm only after your real card fits exactly.