An additional important font measurement is the x-height, or the body height. The body height is the key part of the lowercase letters exclusive of any ascenders or descenders, the part of the letter stuck between the baseline and the “waistline” of the font. This is measured on the lowercase x, which is the most exact letter to determine this measurement, compared to the rest of the letters. The space from the baseline of the x to the top of the x is called the x-height.
The purpose of the x-height is to determine the readability of a font. There is no specific unit of measure. Rather, x-heights are considered small, medium or large. Some fonts have a larger x-height than others, which can make them seem larger than other fonts at the same font size.
The readability of a font can determine its usage for a particular audience. Fonts with large x-heights are typically used for children’s books, since children can recognize the letters more easily. Fonts with medium x-heights are used for most material read by adults. Script fonts often have a small x-height, because the flourishes of the ascenders and descenders are quite long compared to the body height. These are often seen on cards and invitations, and need to be used at a larger size than Roman-style fonts to improve readability.
The fonts below are all at 28 point size. The colored dashed lines show the x-height of each font across the whole line, so you can compare it to the other fonts. The x-height of the first font is nearly twice the size of the last font. The fonts shown are Century Gothic, Adobe Caslon Pro, and Edwardian Script ITC.