What is Leading? - Words and Typography

During the days of metal type, Leading (pronounced ledding, not lee-ding) refered to the strips of lead inserted between the lines of type to fix line spacing. It denotes the total baseline-baseline distance. Too close a leading would make the descenders of the upper line merge into the arms of the ascenders of the lower one and the superscript and subscript characters would almost disappear. Consequently the text becomes too dense to read comfortably.

Similarly, a wide leading too would increase the distance between the lines on your page. Since the space between lines is important both for readability and the overall look of the page, typographic professionals consider leading so vital a factor that while stating the point size, they specify the leading as well.

Computers make it possible for us to try out different values of leading and then decide for the best. Normally, a leading of 120% of the point size is considered proper. Thus, if you ask for 12 point font, the word processing or page layout application you use would automatically produce a leading of 14 or 14.4 points by default. In headlines of higher point size and display text, 120% leading would appear excessive. Multiple-line headline and leaded at 100% or less.