em
em
definition
noun
From there, sizing descendant elements with ems (a relative unit of measurement) becomes much more logical: 1em is 10 px, 1.6em is 16 px, .9em is 9px, and so forth.
a unit for measuring the width of printed matter, equal to the height of the type size being used.
abbreviation
electromagnetic.
example
It doesn't matter which unit you use - zero horseshoes is the same as zero pixels, 'ems' , or percentages.
Sterne was almost compulsively attentive to page layout and typography, going so far as to specify the length of each dash in printer's 'ems' .
So, a font size of 1.25 'ems' will be displayed as 1.25 pixels.
From there, sizing descendant elements with 'ems' (a relative unit of measurement) becomes much more logical: 1em is 10 px, 1.6em is 16 px, .9em is 9px, and so forth.
This reduced the text to an unreadable level when the CSS specified sizes in 'ems' , but only reduced it slightly when specified as percentages.
Credits: Google Translate
