Photography Framing Calculator

Framing a print is a nested-rectangle problem. The mat window is cut to the visible image size, usually a few millimetres smaller so the print edges are held rather than exposed; the outer mat adds border width on all four sides; the moulding adds its face width outside that. Each stage adds twice the relevant width because it applies to both edges, which is why a 16 by 20 inch print with a 3 inch mat and 1.5 inch moulding finishes at 25 by 29 inches. The perimeter figure matters commercially, since moulding is bought by linear length and the 108 inches there is the stock needed before mitre waste. Pixel outputs come from a separate relationship, print inches multiplied by resolution, so 24 by 36 inches at 300 dpi demands 7200 by 10800 pixels, about 77.8 megapixels. Conventional values are worth knowing. Mats of 2 inches suit prints of 8 by 10 and under, 2.5 to 4 inches is normal for larger work, and traditional bottom weighting adds 0.25 to 0.5 inches to the lower border so the image does not appear to sag. The 300 dpi figure is a conservative near-viewing standard; prints seen from two metres hold up at 150 to 200 dpi, cutting the 24 by 36 requirement to around 35 megapixels. Mat and backing board should be acid-free and lignin-free, and the mat partly exists to keep glazing off the emulsion. One caveat: the calculator assumes the image aspect ratio already matches the presentation, since a 3:2 file in a 4:5 window must be cropped.

Window mounts and glazed frames were developed for works on paper long before photography. Print rooms and collectors in eighteenth and nineteenth century Europe used cut card mounts to handle drawings and engravings without touching the sheet, and commercial mount cutting became a trade alongside the framing business. Photographic practice inherited these habits directly: albumen prints of the 1860s were routinely mounted on card because the thin paper support curled, and cabinet cards and cartes de visite were sold as standardised mounted formats. The move to conservation-grade materials is more recent and better documented. Research through the mid twentieth century established that acidic wood-pulp board releases compounds that yellow and embrittle artwork in contact with it, producing the familiar mat burn line along the window bevel. William J. Barrow's deacidification work in the 1950s and 1960s brought paper permanence to wide attention, and the resulting standards, including ISO 18902 and 18916 covering imaging enclosures and the photographic activity test, now define what may be called archival. The American Institute for Conservation and the Library of Congress publish the framing guidance most cited today. Standard retail sizes such as 8 by 10, 11 by 14 and 16 by 20 inches derive from earlier plate and enlarging paper sizes, and the 300 dpi benchmark comes from prepress halftone practice, where a 150 line-per-inch screen was fed at twice the screen frequency.