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=                          Em_(typography)                           =
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                             Introduction                             
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An em (from 'em quadrat') is a unit in the field of typography, equal
to the currently specified point size. For example, one em in a
16-point typeface is 16 points. Therefore, this unit is the same for
all typefaces at a given point size.

The em space  is one 'em' wide.

Typographic measurements using this unit are frequently expressed in
decimal notation (e.g., 0.7 em) or as fractions of 100 or 1000 (e.g.,
em or  em). The number of pixels per em varies depending on system.


                               History                                
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In metal type, the point size (and hence the 'em', from 'em quadrat')
was equal to the line height of the metal body from which the letter
rises. In metal type, the physical size of a letter could not normally
exceed the em.

A digital font's design space in digital type is called the em, which
is a grid with arbitrary resolution. Scaling the em to a particular
point size is how imaging systems—whether for screen or print—work.

In digital type, the relationship of the height of particular letters
to the em is arbitrarily set by the typeface designer. However, as a
very rough guideline, an "average" font might have a cap height of 70%
of the em, and an x-height of 48% of the em.


                   Obsolete alternative definition                    
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In some older texts, but not all, the em is defined, or said to have
been defined, as the width of the capital 'M' in the current typeface
and point size. Possibly, this is because the 'M' (or 'm') sort in
such cases cast the full-width of the quad (also known as 'em quad',
'mutton quad', or 'm quadrat'); and thus, the width of the sort would
equal its point size.

Note however, that in the oldest attested English text from 1683
mentioning em (as 'm' or m quadrat), this alternative definition is
not used, and also not in many other older texts.


                                 CSS                                  
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In Cascading Style Sheets, the 'em' unit is the height of the font in
nominal points or inches. The actual, physical height of any given
portion of the font depends on the user-defined DPI setting, current
element font-size, and the particular font being used.

To make style rules that depend only on the default font size, another
unit was developed: the rem. The rem '«rem Unite»', or root-em, is the
font size of the root element of the document. Unlike the em, which
may be different for each element, the rem is constant throughout the
document.


                               See also                               
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* Em dash (—)
* En (typography)
* Fullwidth forms
* List of XML and HTML character entity references
* Non-breaking space width variations
* Responsive web design
* Whitespace characters
* Point «pt» (typography)
* Pica «pc» (typography)
* Pixel (px)
* Centimetre (cm)
* Measurement (mm)
* Micrometre (UM-µm)


                            External links                            
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* [http://www.corelangs.com/css/basics/units.html CSS Length and
Units]
* [https://lyty.dev/css/css-unit.html CSS Units and Values]
* [https://www.w3.org/WAI/GL/css2em.htm The amazing em unit and other
best practices]
* [https://cssunitconverter.com/px-to-em/ PX to EM Converter with Live
Text Preview]


 License 
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL: http://creativecommons.org/licenses/by-sa/3.0/
Original Article: http://en.wikipedia.org/wiki/Em_(typography)


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