The Definition of 'Leading' in Typography and Page Layout

Typescript metal letters

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The term leading dates to the days of hot metal type when strips of lead were placed between rows of type to provide line spacing. Leading is the space between the baseline of one line of type and the baseline of the next line of type. It is usually expressed in points.

The greater the leading, the further apart the lines of type are spaced. Changing the leading of text affects its appearance and readability. Some fonts read better with increased leading due to long ascenders and descenders. 

There is no one formula for figuring how much leading to use in a document. Although a column of 10 point type might look just fine with 12 point leading, a 24 point script with elaborate descenders might need 30 or more points of leading to look right.

Spacing out a section of text is easy to do by increasing the leading. This airy treatment of text calls attention to it and should be used only when the design calls for it. Changing the leading arbitrarily within an otherwise-consistent section of text is likely to distract the reader and is usually a symptom of poor design. 

It is possible to use such a small amount of leading that the descenders of one line touch the ascenders of the line beneath it. In this case, it is best to increase the leading a little for legibility.

Some software may use the term line spacing while others still refer to leading. Word processing software often has the option to use single, double or even triple spacing, or to specify specific leading in points or other measurements. Some software has a feature called auto leading which calculates leading automatically. Programs that offer automated leading calculate leading based on the text size. When a line of type includes more than one type size, this automatic leading can result in odd or inconsistent line spacing.