Picture Frame Size Calculator

A framing package is a stack of concentric rectangles, so the arithmetic is purely additive: every layer adds twice its own width, once on each side. Artwork 8 by 10 inches with a 2 inch mat border becomes a 12 by 14 inch mat board, and a 1 inch molding brings the outer dimension to 14 by 16 inches. Glass and backing are cut to the mat outer size rather than the outer frame size, because they seat in the rabbet, the L-shaped channel milled into the back of the molding, typically 1/4 to 3/8 inch deep. Molding is sold by the linear foot, so perimeter drives frame cost, while glazing is priced by the square foot of area. Framers size mats proportionally rather than by a single rule: roughly 1.5 to 2 inches for prints up to 5 by 7, 2 to 3 inches for 8 by 10 through 11 by 14, and 3 inches or more for 16 by 20 and larger. Many shops bottom-weight the mat by adding about half an inch to the lower border, which counters the optical illusion that evenly matted work sits low in its frame. The window opening is normally cut about 1/4 inch smaller than the sheet on each side so the mat overlaps and supports the paper. The main caveats are that this model assumes a plain rectangular opening, ignores the rabbet lip that hides roughly 1/8 to 1/4 inch of the glazing edge, and does not describe ready-made frames, which are labelled by the art size they accept rather than by their outer dimensions.

Framing became a separate craft in Italian panel painting. Early fourteenth-century altarpieces were carved and gilded as a single unit with their surrounds, and only during the fifteenth century did the frame become a detachable object produced by specialist carvers and gilders in Florence and Venice. The mat, or passe-partout, is a later and more modest invention tied to the spread of works on paper: engravings, watercolours and, from the 1840s, photographic prints all needed a spacer to hold the sheet off the glass. Nineteenth-century printsellers cut those spacers from wood-pulp board, which is acidic and produced the brown mat-burn line still visible on the edges of many Victorian prints. The standards used today are twentieth-century. Cotton rag and buffered alpha-cellulose boards were introduced by conservation suppliers after mid-century, and preservation guidance from the Library of Congress and comparable national institutions made acid-free board and reversible hinges of Japanese tissue and starch paste the norm for anything of value. The familiar sizes came from the photographic trade, where Kodak print formats fixed 4 by 6, 5 by 7, 8 by 10 and 11 by 14 inches in the United States, while ISO 216, published in 1975 and derived from the German DIN 476 standard of 1922, gave Europe the A-series and its metric frame sizes. Ultraviolet-filtering and anti-reflective glazing are recent additions, with museum-grade products now blocking roughly 99 percent of UV.