What is the unit of magnification?

Magnification is the increase (or reduction) in the size of an optical system-produced picture relative to its actual size. Although angular magnification is seldom encountered, linear magnification is the most often used type of magnification. the standard representation of power as a measure of magnification. More generally, the symbol or x is used to denote that a measurement is a multiple of a standard or reference measurement by adding its mathematical meaning of "times" to it.
It is actually pretty easy to calculate the total magnification of an image you are viewing through a microscope.To get the total magnification take the power of the objective (4X, 10X, 40x) and multiply by the power of the eyepiece, usually 10X.