aspect ratio

n.

1. The width-to-height ratio of a film or television image.
2. The span-to-mean-chord ratio of an airfoil.

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As originally conceived, the ratio of the span of a wing or airfoil to the chord of a wing, where the span is the maximum cross-stream dimension and the chord is the dimension in the streamwise direction, as illustrated. This definition is unambiguous only in the case of a rectangular wing.

Because early wings were usually nearly rectangular, no confusion resulted from the original definition. Later, when wings were tapered or had complex planforms, another definition became necessary. It was desirable that the new and more general definition correspond to the old definition for the special case of the rectangular wing. The more general definition of geometrical aspect ratio which is now universally used is given in the equation below, where A is the aspect ratio and b and S are defined in the illustration. Because S is equal to bc for a wing of rectangular planform, the definition of aspect ratio given in the equation corresponds to the original idea of the ratio of the span to the chord for a rectangular wing.

Aspect ratio of a wing.

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The ratio of width to height of an object. Stating the relationship of one side to the other, it is widely used to describe the shape of a TV or computer screen. For example, the aspect ratio of a standard screen is 4:3, which is a relatively square rectangle. The 4:3 means "4 to 3," or four units wide to three units high. High-definition TV (HDTV) has a 16:9 ratio, which is a wide rectangle closer in width, but still not as wide, as most cinema screens.

Another way of expressing the 4:3 and 16:9 ratios is 1.33:1 and 1.78:1, but these latter designations are used mostly for cinema formats, not TV (see below).

Standard or Wide Screen?

The common measurement of a computer monitor or TV is the screen's diagonal measurement in inches. However, a 20" screen does not disclose whether its layout is 4:3 (square) or 16:9 (wide). See letterbox, resolution, HDTV display modes and anamorphic DVD.

Standard and HDTV Aspect Ratios

Fitting the wide screen HDTV image (16:9) on the right into a standard TV (4:3) on the left creates the "letterbox effect" (black bars on top and bottom). (Image courtesy of Intergraph Computer Systems.)

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Ratio between the width and the height of a television or motion picture screen. This ratio is important to the person responsible for photographing products to be shown in a commercial, so that these products may be shown in their most flattering perspective.

1. In any rectangular configuration (such as the cross section of a rectangular duct), the ratio of the longer dimension to the shorter.
2. In a rectangular configuration, the ratio of the long-side to the short-side.

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For a list of words related to aspect ratio, see:

• Cinematography Tools and Techniques - aspect ratio: ratio of width of a projected image to its height

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