Line length is the dis­tance be­tween the left and right edges of a text block. Overly long lines are a com­mon prob­lem, but they’re easy to cor­rect. Shorter lines will make a big dif­fer­ence in the leg­i­bil­ity and pro­fes­sion­al­ism of your layout.

The most use­ful way to mea­sure line length is by av­er­age char­ac­ters per line. Mea­sur­ing in inches or cen­time­ters is less use­ful be­cause the point size of the font af­fects the num­ber of char­ac­ters per inch. Whereas char­ac­ters per line works at any point size.

Shorter lines are more com­fort­able to read than longer lines. As line length in­creases, your eye has to travel far­ther from the end of one line to the be­gin­ning of the next. Aim for an av­er­age line length of 45–90 char­ac­ters, in­clud­ing spaces. You can check line length us­ing word count.

Al­ter­na­tively, use the al­pha­bet test to set line length. This rule of thumb is worth mem­o­riz­ing, as it can be used even in the ab­sence of a word-count func­tion. You should be able to fit be­tween two and three al­pha­bets on a line, like so:

abcde­fghijklmnopqrstu­vwxyz­abcde­fghijklmnopqrstu­vwxyz­abcde­fgh
= 2.31 alphabets

How do you ad­just line length? Gen­er­ally you’ll want to es­tab­lish the ba­sic length us­ing page mar­gins. True, you can also set the side in­dents of a para­graph through para­graph-level for­mat­ting, but you should re­serve that for spe­cial sit­u­a­tions (for in­stance, block quo­ta­tions).