Mat borders, overlap and a weighted bottom

A mat has an outside size, an opening and borders between them. The opening is smaller than the artwork, because the mat overlaps its edge on each side so the picture is held in place and no bare edge shows; a quarter of an inch is common and one framing calculator uses half a centimeter. The border is the visible mat from the edge of the opening to the edge of the mat, and the outside size is the opening plus a border on each side.

One framer's guide suggests borders of at least a third of the artwork's shorter side, about half of it for small art under five by seven inches, and a quarter to a fifth for very large art, never wider than half. Dark mats look wider, so the same guide adds a quarter to half an inch for them. These are guidelines, and contemporary framing often uses equal borders.

A weighted bottom makes the bottom border a little wider than the top and sides. The guide gives half an inch as conservative, three quarters as moderate and a full inch as traditional. In the tool the extra is added to the bottom border only. If you already own a mat, the tool works the other way: it takes the outside size, subtracts the opening and splits what is left between the sides and the top and bottom.

Chart: outside mat width by artwork width and border (artwork ten inches high)

Each cell is the outside width of the mat for the artwork width in its row and the border in its column, with a quarter inch of overlap. The height follows the same way from the artwork height.

	Border width
Artwork width	1.5 in	2 in	2.5 in	3 in	4 in
5 in	7.50 in	8.50 in	9.50 in	10.50 in	12.50 in
8 in	10.50 in	11.50 in	12.50 in	13.50 in	15.50 in
11 in	13.50 in	14.50 in	15.50 in	16.50 in	18.50 in
16 in	18.50 in	19.50 in	20.50 in	21.50 in	23.50 in
20 in	22.50 in	23.50 in	24.50 in	25.50 in	27.50 in
24 in	26.50 in	27.50 in	28.50 in	29.50 in	31.50 in

Work out your own numbers: Picture mat size and border planner

Chart: opening height by artwork height and overlap (artwork eight inches wide)

Each cell is the height of the opening to cut for the artwork height in its row and the overlap in its column. The opening is the artwork less the overlap on both sides.

	Overlap on each side
Artwork height	0 in	0.25 in	0.5 in
7 in	7.00 in	6.50 in	6.00 in
10 in	10.00 in	9.50 in	9.00 in
14 in	14.00 in	13.50 in	13.00 in
20 in	20.00 in	19.50 in	19.00 in

Work out your own numbers: Picture mat size and border planner

Used by

• Picture mat size and border plannerMat size, opening and borders for a framed picture.

Sources

• Custom Picture Frames: border width proportions and weighted bottom borders
• Profile Products mat border calculator: overlap of the mat on the artwork