Characters per line

In typography and computing characters per line (CPL) or terminal width refers to the maximal number of monospaced characters that may appear on a single line. It is similar to line length in typesetting.

History

The limit of the line length in 70–80 characters may well be originated from various technical limitations of various equipment. The American teletypewriters could type only 72 CPL, while the British ones even less, 70 CPL. In the era of typewriters, most designs of the typewriter carriage were limited to 80–90 CPL. The most widespread and standard paper size in the US (8.5×11") also has been imposing limitations on the line length: it is possible to print only 85 or 102 characters (with the font size either 10 or 12 characters per inch) without margins on the typewriter. With various margins (usually from 1 to 1.5 inches for each side, but there is no strict standard) these numbers may shrink to 55–78 CPL.

In computer technology, a line of an IBM punched card could consist of only 80 characters. The widespread computer terminals such as IBM 3270 followed this limitation, their monitors could show only 80 CPL (but with the various number of lines), with some model this number was either reduced by half to 40 CPL or increased to 132 CPL. Such line lengths have been carried over into text modes of personal computers.