Em Space on:
[Wikipedia]
[Google]
[Amazon]
An em (from '' em quadrat'') is a unit in the field of
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
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.This alternative definition is shown in th
Adobe Glossary
and the Pocket Oxford Dictionary Third revised edition 1996. Possibly, this is because the 'M' (or 'm') sort in such cases cast the full-width of the
CSS Length and Units
{{Typography Display technology Typography Units of length
typography
Typography is the art and technique of Typesetting, arranging type to make written language legibility, legible, readability, readable and beauty, appealing when displayed. The arrangement of type involves selecting typefaces, Point (typogra ...
, equal to the currently specified point size. It corresponds to the body height of the typeface
A typeface (or font family) is a design of Letter (alphabet), letters, Numerical digit, numbers and other symbols, to be used in printing or for electronic display. Most typefaces include variations in size (e.g., 24 point), weight (e.g., light, ...
. 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
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
In typography, cap height is the height of a capital letter above the baseline for a particular typeface
A typeface (or font family) is a design of Letter (alphabet), letters, Numerical digit, numbers and other symbols, to be used in printing ...
of 70% of the em, and an x-height of 48% of the em.
Obsolete alternative definition
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.This alternative definition is shown in thAdobe Glossary
and the Pocket Oxford Dictionary Third revised edition 1996. Possibly, this is because the 'M' (or 'm') sort in such cases cast the full-width of the
quad
QUaD, an acronym for QUEST at DASI, was a ground-based cosmic microwave background (CMB) polarization experiment at the South Pole. QUEST (Q and U Extragalactic Sub-mm Telescope) was the original name attributed to the bolometer detector instrume ...
(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
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 unit»'', 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
*Em dash
The dash is a punctuation mark consisting of a long horizontal line. It is similar in appearance to the hyphen but is longer and sometimes higher from the baseline. The most common versions are the endash , generally longer than the hyphen ...
(—)
* En (typography)
An en (from English '' en quadrat'') is a typographic unit, half of the width of an em. By definition, it is equivalent to half of the body height of the typeface (e.g., in 16- point type it is 8 points). The en is sometimes referred to as th ...
* Fullwidth forms
* List of XML and HTML character entity references
* Non-breaking space width variations
* Responsive web design
Responsive web design (RWD) or responsive design is an approach to web design that aims to make web pages render well on a variety of devices and window or screen sizes from minimum to maximum display size to ensure usability and satisfactio ...
* Whitespace characters
A whitespace character is a character (computing), character data element that represents White space (visual arts), white space when text string, text is
Rendering (computer graphics), rendered for display by a computer.
For example, a ''Space ...
* Point «pt» (typography)
* Pica «pc» (typography)
* Pixel (px)
* Centimetre (cm)
* Measurement (mm)
* Micrometre (UM-μm)
References
External links
CSS Length and Units
{{Typography Display technology Typography Units of length