First calibrate the screen: place a standard bank/credit card on the dashed box and adjust the slider until the box exactly matches the card’s width (85.6 mm).
Match a credit card to this box
Now place an existing ring over the circle and adjust until the inner edge lines up:
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Wrap a strip of paper or string around the base of your finger, mark where it overlaps, and enter the length in millimetres:
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Tip: measure at the end of the day when fingers are largest, and avoid measuring when cold.
Download and print our vector-perfect ring sizer at 100% scale (no fit-to-page). Cut out the strip and wrap it around your finger.