22.3.3 Line Spacing
Line spacing refers to the vertical distance between the base of 1 line of text and the base of the next line of text. Line spacing is traditionally known as leading for the strips of lead once used between lines of printer type. The space between lines of type is measured in points. Generally, leading is 20% larger than the copy size.3 For example, 10-point copy would be set on 12 points of leading or line spacing (10/12), as is shown for the body copy in Figure 1. Optimal line spacing requires consideration of the type size, layout density, and line length. Generally, longer lines call for increased line spacing for optimal readability. See Figure 7 for different examples of changes in line spacing that change the appearance of the text. More open line spacing also calls for wider margins; tighter line spacing can be done within narrower margins.
The conventions for letterspacing and word spacing vary depending on the amount of spacing between lines, column width and depth, and whether the text is justified (set as a squared-off block) or unjustified (set with a ragged right margin). For example, a smaller type size may be used on a wider column if the line spacing is adequate for readability. The nature of the composed material will suggest whether variations in typography may be effectively used.