In typography and computing, characters per line ( CPL) or terminal width refers to the maximal number of Monospaced font characters that may appear on a single plain text. It is similar to line length in typesetting.
The limit of the line length in 70–80 characters may well have originated from various technical limitations of various equipment. The American
could type only 72 CPL, while the British ones even less, 70 CPL.
In the era of
, most designs of the typewriter carriage were limited to 80–90 CPL. Standard paper sizes, such as the international standard A4, also impose limitations on line length: using the US standard Letter paper size (8.5×11"), it is only possible to print a maximum of 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 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 consisted of 80 characters. Widespread computer terminals such as DEC's VT52 and VT100 mostly followed this standard, showing 80 CPL and 24 lines. This line length was carried over into the original 80×25 text mode of the IBM PC, along with its clones and successors. To this day, virtual terminals most often display 80×24 characters.
The "long" line of 132 CPL comes from mainframes' .
However, some printers or printing terminals could print as many as 216 CPL, given certain extra-wide paper sizes and/or extra-narrow font sizes.
In modern computing
With the advent of desktop computing and publishing, and technologies such as TrueType
used in word processor
and web browser
, a uniform CPL has been made mostly obsolete. HTML
(and some other modern text presentation formats) uses dynamic
which is more flexible than characters per line restriction and may produce a text block with non-rectangular shape, just like in paper typesetting
Many plain text documents still conform to 72 CPL out of tradition (e.g., ).
Many style guides for computer programming define the maximum or desirable number of characters in a line of source code
IBM 80-column punched card format
Apple 80-Column Text Card
Line length (the equivalent concept for non-monospaced text)