Em (typography)
An em is a unit of measurement in the field of typography, equal to the currently specified point size.
The name of em is related to M. Originally the unit was derived from the width of the capital "M" in the given typeface.
This unit is the same for all fonts at a given point size.
One em in a 16 point typeface is 16 points. 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. 70/100 em or 700/1000 em.
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