The card sets the scale
The long edge of an ISO ID-1 payment card is 85.60 mm. Two clicks translate photo pixels into approximate millimeters at the card's plane.
A private calibrated photo tool
Put the stone on your hand before the ring exists.
A standard card gives the photo a physical scale. Mark its long edge, tap your ring finger, and preview the selected diamond's approximate face-up footprint on your own hand.
No accountNo photo uploadExports on your device
Your photo stays here.
Choose a hand photo from the controls. It is decoded, calibrated, rendered, and exported inside this browser tab.
Camera angle still matters
The card and finger must be flat on the same surface, with the camera directly above them. Perspective, lens distortion, and finger curvature can change the apparent scale.
The footprint is literal
Facet uses typical face-up dimensions for the chosen shape and carat. It does not simulate prongs, band width, setting height, sparkle, color, or exact stone proportions.