Line length for text

a line in a book shouldn't run to more than about 27 picas (four and a half inches) because if you have more than about 54en, or characters (27em), to a line the eye tends to have difficulty finding the next line.

http://www.microsoft.com/typography/glossary/ch6.htm

The ideal line length for text layout is based on the the physiology of the human eye... At normal reading distance the arc of the visual field is only a few inches - about the width of a well-designed column of text, or about 12 words per line. Research shows that reading slows and retention rates fall as line length begins to exceed the ideal width, because the reader then needs to use the muscles of the eye and neck to track from the end of one line to the beginning of the next line. If the eye must traverse great distances on the page, the reader is easily lost and must hunt for the beginning of the next line. Quantitative studies show that moderate line lengths significantly increase the legibility of text.

Web Style Guide - Basic Design Principles for Creating Website
Patrick J. Lynch and Sarah Horton
2nd edition, page 97.

see also: Ideal line length for content, Russ Weakley May 3, 2003

mxt

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