In typography, x-height is the distance between the baseline of a line of type and tops of the main body of lowercase letters (i.e. excluding ascenders or descenders). The x-height is a factor in typeface identification and readability.
Typefaces with very large x-height relative to the ascender and cap height of the font have shorter ascenders and descenders and thus less white space between lines of type. Sans serif typefaces typically have large x-heights.
Issues With X-Height
In typefaces with small x-heights, other letter parts such as ascenders and descenders may become more visually noticeable.
Typefaces with large x-heights may appear darker, heavier, crowded, and more difficult to read at body copy sizes.
Also Known As: z-height
Alternative Spelling: xheight
Common Misspellings: x-hieght