Multi-opening mat calculator
Find the outer board for a regular grid of equal mat windows.
Choose your measurements and calculate to see the result.
Save these dimensions
This site keeps one project slot in this browser. Saving again updates that slot. Export the project file for a dependable backup.
A visual size estimate. Verify the actual artwork, frame, mat, glazing, hardware, wall and manufacturer specifications before buying or arranging a display. Dimensions alone do not guarantee fit.
Size the windows and the spaces between them.
This tool calculates a board for identical rectangular openings arranged in rows and columns. The inner gap is measured between window edges; the outer border runs from the outermost window to the board edge.
Board width = columns × window width + inner gaps + 2 × outer border
Worked example: four 4 × 6 photos
At ⅛ inch overlap per edge, each window is 3¾ × 5¾ inches. A 2 × 2 arrangement with 1 inch inner gaps and 2 inch outer borders needs a 12½ × 16½ inch board.
The window layout does not prove that the full prints fit independently behind the board. Their hidden borders may overlap. Confirm full sheet sizes, supplier web-width limits, backing dimensions and the actual frame opening. Use the single-window calculator to derive each opening.