X-height
Also called: x-height or ex
The typographical term x-height refers to the height of the lowercase letters, without sticks and tails. The x-height indicates how high the lowercase letters of a font are in relation to the uppercase letters.
The term refers to the height of the letter x, which in most fonts corresponds to the u, v, w, and z. The height of the a, c, e, m, n, o, r, and s, because of their curvature, often differs slightly from the x-height. Lowercase letters whose lowercase letter is higher than the x-height are called stick letters or tail letters.
High or low x-height?
In general, texts in fonts with a relatively large x-height are easiest to read. For this reason, such fonts are widely used on signs that must be read from a great distance. High x-height fonts are also widely used in newspapers because they allow more text to be printed on one page while maintaining legibility.
The disadvantage of a high x-height is that upper and lower case letters are less easily distinguishable and a text appears "blacker. This can actually make a text less readable.
X-height in web design
In web design, x-height is denoted in the unit ex. Like em, this unit can be used to define the size of elements according to the chosen font size. Where em corresponds to the chosen size of letters in points, ex corresponds to the resulting x-height.
