Definition: aspect ratio

The aspect ratio states the comparison of width to height and is commonly used to describe the shape of a TV or computer screen. For example, the aspect ratio of an earlier standard-definition (SD) screen was 4:3, which is a relatively square rectangle. The 4:3 means "4 to 3," or four units wide to three units high. Today's TVs and monitors typically have a 16:9 ratio, which is a wide rectangle that is still not as wide as most movie theater (cinema) screens.

Another way of expressing the 4:3 and 16:9 ratios is 1.33:1 and 1.78:1; however, these latter designations are used mostly for cinema formats, rather than TV (see illustration below). See letterbox, screen resolution, HDTV display modes and anamorphic DVD.

The 2.39:1 Is Also 2.4:1

The anamorphic scope aspect ratio of 2.39:1 is commonly rounded up to 2.4:1.

Cinemascope on an iPhone

Moment created an anamorphic lens for an iPhone with a 2.4:1 aspect ratio in order to simulate a Cinemascope video on a smartphone. (Image courtesy of Moment, Inc.)

The Letterbox Effect

Displaying a wide screen 16:9 image (right) on a standard-definition 4:3 TV (left) creates black bars on the top and bottom. Movies that retain their original, extra-wide cinema formats will create a letterbox even on today's wide screen TVs. (Image courtesy of Intergraph Computer Systems.)