X-height is the vertical distance from a typeface’s baseline to the top of its lowercase letters. Imagine lowercase letters standing on a shared floor: x-height measures how tall their main bodies rise. A medium-to-large x-height, often more than half the font size, usually supports readable text on small screens. section 20.3
When auditioning a typeface, check x-height alongside these related features:
- Large counters and apertures leave letter shapes more open and legible. section 20.3
- Low-to-medium stroke contrast keeps extremely thin strokes from disappearing on small screens. section 20.3
- Pair typefaces only when their legibility characteristics—including x-height—work harmoniously. section 20.3
A quick typeface check
Open Google Fonts, view a typeface, and try lowercase letters such as x, o, a, e, g, and y. Compare their apparent body height and readability, then look for an x-height greater than half the font size. section 20.3
