The ratio of width to height of an object. (Width divided by
Height= Aspect Ratio )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).