Aspect Ratio Calculator

An aspect ratio states the proportion between width and height, and reducing the pair by their greatest common divisor gives the canonical form. For 1920 by 1080 the GCD is 120, yielding 16:9 and a decimal of 1.7778; the diagonal, by Pythagoras, comes to 2203.4 px. Reduction is exact but not always informative, because arbitrary dimensions produce awkward results: 1366 by 768 reduces to 683:384, a decimal of 1.7786 that no one names, though it sits close enough to 16:9 that panels are sold as widescreen. This is why the decimal value, not the reduced integer pair, is the practical comparison tool, and why matching against a table of named ratios with a tolerance is more useful than exact reduction. One distinction causes persistent confusion. Storage aspect ratio describes the pixel grid, while display aspect ratio describes the shape on screen, and they diverge whenever pixels are not square. Standard-definition DV at 720 by 480 has a storage ratio of 1.5 but a pixel aspect ratio near 0.9, so it displays as 4:3; anamorphic cinematography squeezes a 2.39:1 image onto a narrower frame and unsqueezes it in projection. Mismatches between source and target ratios must be resolved by letterboxing, which adds bars and preserves the whole frame, or by cropping, which fills the frame and discards content. Common ratios in use are 16:9 for broadcast and streaming, 3:2 for full-frame stills, 4:5 and 1:1 for social feeds, 9:16 for vertical video, and 2.39:1 for anamorphic cinema.

The oldest standard ratio came from the film gauge itself. When William Kennedy Dickson laid out 35mm film for Thomas Edison in the early 1890s, four perforations per frame produced an image close to 4:3, and that 1.33 proportion carried into silent cinema and, later, into television. Adding an optical soundtrack in the late 1920s ate into the frame width, and the Academy of Motion Picture Arts and Sciences responded in 1932 by standardising the Academy ratio of 1.375:1. Studios reached for wider frames in the 1950s to differentiate cinema from television: CinemaScope arrived in 1953 using anamorphic lenses, while 1.85:1 became the American flat standard and 1.66:1 the common European one. Television inherited 4:3 and kept it for decades, which made the choice of a successor contentious. Kerns H. Powers, working at the David Sarnoff Research Center, proposed 16:9 in the mid-1980s on the reasoning that it was roughly the geometric mean of the ratios then in circulation, so that every existing format could be fitted inside a common rectangle with the least wasted area. SMPTE and later ITU-R adopted 16:9 for high definition, and BT.709 fixed it for HDTV. The most recent shift came from hardware in people pockets: smartphones after 2007 were held upright, and platforms built around vertical video made 9:16 a production standard rather than an accident of orientation.