Will two different-sized prints fit my existing frame?
Measure the insert that actually fits the frame, not its outside dimensions or the visible front opening. For 10 × 15 and 15 × 10 cm prints with 0.5 cm overlap and a 2 cm opening gap, the combined windows span 25 × 14 cm side by side. A 35 × 24 cm insert with 2 cm extra at the bottom leaves 5 cm side borders, 4 cm at the top and 6 cm at the bottom. The calculator keeps both print sizes unchanged and rejects a frame that cannot contain the hidden paper edges.
Two openings are different from two mat layers
This layout contains two pictures in one mat board. A double mat uses two board layers around an image and needs separate reveal and cutting settings. The calculator addresses the first task only.
Allow for the paper hidden behind the mat
An overlap of 0.125 inch on each edge reduces both window dimensions by 0.25 inch. The same overlap also uses space behind the gap between windows. For example, a 1 inch opening gap leaves 0.75 inch between the complete print edges. Logan’s multiple-opening guidance explains why windows should be smaller than the prints they hold.
Logan: multiple-opening mat measurements ↗
Use the front-view coordinates consistently
Opening positions are measured rightwards and downwards from the board’s front top-left corner. A smaller photograph is centered on the shared cross-axis. If you mark the board from behind, the layout must be transferred correctly and the cutter’s own bevel instructions still apply. The scaled diagram is a planning view, not a full-size template.
The result is the mat insert size and visible opening geometry. Confirm the frame’s internal fit, the measured prints and your cutter settings before cutting.