In typography, line length is the width of a block of typeset text, usually measured in units of length like inches or points or in characters per line (in which case it is a measure). A block of text or paragraph has a maximum line length that fits a determined design. If the lines are too short then the text becomes disjointed; if they are too long, the content loses rhythm as the reader searches for the start of each line.

Line length is determined by typographic parameters based on a formal grid and template with several goals in mind: balance and function for fit and readability with a sensitivity to aesthetic style in typography. Typographers adjust line length to aid legibility or copy fit. Text can be flush left and ragged right, flush right and ragged left, or justified where all lines are of equal length. In a ragged right setting, line lengths vary to create a ragged right edge. Sometimes this can be visually satisfying. For justified and ragged right settings typographers can adjust line length to avoid unwanted hyphens, rivers of white space, and orphaned words/characters at the end of lines (e.g., "The", "I", "He", "We").