Gather a glass cutter, straightedge, marker, measuring tape, safety glasses, gloves, and a flat work surface
Measure and mark the cut line on the mirror’s backing
Clean the mirror surface thoroughly
Place the mirror on a flat, stable surface with the backing facing up
Align the straightedge with the marked cut line
Score the mirror once with firm, even pressure using the glass cutter
Avoid scoring the same line multiple times
Place the scored line over the edge of a table or use running pliers
Apply even pressure to snap the mirror along the score
Smooth sharp edges with fine sandpaper or a glass stone
Wear gloves and handle the cut mirror carefully