em (pleading)

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The unit of measurement em is used in typesetting to determine the character width depending on the font size . A em corresponding to the width of an em space ( English quad ) of the printing system. That is, although it is widely asserted, not exactly - but only about - the width of the capital letter M . The width of the em quarter corresponds to the height of the em quarter and thus the font size - an em is therefore directly proportional to the font size, regardless of the design of the capital letter M of the respective font . For the half square en stands .


When displaying text documents, there are two criteria relating to the width of a column that make reading a text easier or more difficult for the reader:

  • Lines that are too long make it difficult to find the next line after the line break.
  • Lines that are too short lead to larger spaces at the end of lines.

A comfortably legible typeface can be defined by defining the width in em regardless of the font size. The length of the line changes with the size of the font, which preserves the typeface.

Application for website presentations

The unit em is also important when displaying websites . The appearance of the text can be defined by the web designer independently of the web browser- based font size settings, in contrast to absolutely defined widths, which in extreme cases can cause the problems mentioned above.

The CSS standard, which is important for the design of websites, defines an em in accordance with the general definition mentioned in the introduction as the current font size of the font in pixels.

In addition to determining the line width, Em can also be used in CSS to define the font size and line height.


  • font-size: 2em; (in German: font size 2em) doubles the font size.
  • line-height: 1.2em; (in German: line spacing 1,2em) sets the line spacing to 120% of the font size. Between the lines, that is, 20% of the font size is called Bullet released.

CSS also defines a unit rem , the font size of the root element (usually <html>) in em .

Web links

Individual evidence

  1. The height of the square is the minimum line spacing and not the visually perceptible size of letters. In an Antiqua typeface that was customary at the time, the capital letter M (including the distance to the neighboring letters) happened to be about as wide as the line height. In American typography, this was called the M value for short.
    With modern sans serif fonts, there is no longer any direct reference to the height or width of capital letters; the unit means the recommended minimum line height. In contrast to lead letters, however, phototypesetting , especially with computer fonts, can be operated with any line heights up to partial or complete overprinting.
  2. CSS Values ​​and Units Module Level 3. Accessed June 15, 2018 (English).