capheight

Cap height is the distance from the baseline to the top of the capital letters in a typeface. It is a key typographic metric that describes the vertical size of uppercase glyphs independent of the overall point size.

Cap height is contrasted with x-height, which is the height of the body of lowercase letters such as x; ascender height, which is the distance from the baseline to the top of lowercase letters with ascenders (b, d, h); and the cap line, an implied line marking the cap height.

Measurement and variability: In font design, cap height is defined in the font’s metrics, typically in em units, where available. Not every font exposes a capHeight value; designers often estimate by the top of uppercase glyphs like H. Cap height varies widely between typefaces, and diacritics such as accents or umlauts may extend above or below the cap height, affecting the visible height of uppercase characters.

Usage: Cap height affects line height, optical alignment, and the legibility of all-cap settings. When mixing fonts or typefaces with different cap heights, designers adjust leading and vertical rhythm to maintain a cohesive appearance.

In digital typography, cap height is generally not directly controlled by CSS; fonts expose metrics via OpenType tables, and some platforms or font editors provide explicit cap height information. Understanding cap height helps designers compare typefaces and predict how uppercase content will occupy vertical space in a layout.