Three Sizes: Ordering Glass, Mat and Frame

Ordering glass, a mat and a frame means knowing three different sizes, and they are all different from the size of the art.

Three sizes, in order

The frame and mat calculator returns all three because each one is ordered from a different supplier:

• The mat window — slightly smaller than the art, so the mat overlaps and holds its edges
• The outer mat board — which is also the glass and backing size, and what the frame's rabbet must accept
• The outer frame — the finished piece, once the moulding is added

For an 8×10″ print with a 2″ mat border and a 1.5″ moulding: a 7.5×9.5″ window, an 11.5×13.5″ mat and glass, and a 14.5×16.5″ finished frame.

The window is smaller than the art

By default the calculator laps the mat a quarter inch onto the art on each edge, taking an 8″ width down to a 7.5″ window. Cut the window to the art's exact size and the print falls through; the overlap is what holds it.

That overlap also means the outer mat is measured out from the window, not from the art — which is why an 8×10 with a 2″ border comes to 11.5″ rather than the 12″ people expect. It is a small difference and it is the difference between glass that fits and glass that does not.

The mat outer size is the glass size

The number to give a glazier. Mat board, glass and backing are all cut to the same dimension, and the frame's rabbet holds that stack.

Order glass slightly undersized rather than exact — a hair of clearance lets it drop in. Glass cut a millimetre too large will not go in at all, and it cannot be trimmed once cut.

Border width drives everything downstream

Changing the mat changes the glass and the frame. On an 11×14″ print with a 1.25″ moulding:

• 1.5″ mat → 13.5×16.5″ glass, 16×19″ frame
• 2″ mat → 14.5×17.5″ glass, 17×20″ frame
• 2.5″ mat → 15.5×18.5″ glass, 18×21″ frame
• 3″ mat → 16.5×19.5″ glass, 19×22″ frame

Each half inch of border adds a full inch in each dimension, because it appears on both sides. Which is worth knowing before deciding the mat looks a bit narrow.

The finished size is the one for the wall

The outer frame dimension is what the wall sizing and spacing calculators want. Planning a gallery wall from the print size rather than the finished size is how a row that fitted on paper turns out three inches too wide.

The gap between the two is substantial: an 8×10 print finishes at 14.5×16.5 with a modest mat and moulding, nearly doubling in each direction.

Measure the moulding's face

Give the calculator the moulding’s face width: the part you see head-on, not its depth and not the rabbet cut into the back. Suppliers usually list it as face width or simply width, with depth given separately.

If you have a physical sample, lay it face down and measure from the outer edge to the inner lip. That is the number.