Mat Board Calculator — Opening & Border Sizes

The mat opening should be slightly smaller than the print — typically 3-5mm overlap on each side. This overlap holds the print in place behind the mat and ensures no white paper edge shows through. Too much overlap hides important image content.

Traditionally, yes. A slightly wider bottom border (1-2cm extra) compensates for an optical illusion where centred images appear to sag downward. This is called bottom weighting. For a modern, clean look, equal borders all around also works well.

For gallery presentation, 5-8cm borders are standard. Smaller prints (A4 and under) suit 5cm borders. Larger prints (A3+) suit 6-8cm. Very large exhibition prints may use 10cm+ borders. The border should frame the image without overwhelming it.

White or off-white mats are the safest choice and suit most images. Cream/ivory works well with warm-toned or vintage images. Black mats create a modern, dramatic look. Coloured mats should complement the image without competing with it. Always use acid-free mat board for archival framing.

No — board thickness has no effect on the flat (planar) opening or outer dimensions, which are purely a 2D layout. Thickness does matter for the frame rebate (the recess that holds everything): the frame must be deep enough for the glazing, the mat, the print and a backing board. Standard 4-ply conservation mountboard is about 1.4mm; 8-ply museum board is roughly 3mm. This calculator reports the minimum rebate depth so you can check your frame will close.