Typesmetrics

Typesmetrics is a term used in typography and digital typesetting to describe the collection of quantitative measurements that govern the layout and rendering of text. It covers vertical metrics that determine the height of glyphs on a line, horizontal metrics that affect character spacing, and related measures used by layout engines to maintain consistency across fonts and platforms. Core components include ascent, descent, and line gap; cap height and x-height; advance width and side bearings; and kerning values that adjust spacing between specific character pairs.

In digital fonts, these metrics are encoded in font tables, most notably in OpenType; horizontal metrics are stored in the hmtx table, horizontal header in hhea, and broader vertical metrics in the OS/2 and related tables. Metrics are defined in font units (upem) and are scaled by the current font size to produce device or CSS pixel measurements. These metrics influence vertical rhythm (line height) and horizontal rhythm (letter and word spacing), as well as glyph alignment and justification.

Practically, typesmetrics inform how text blocks are laid out in word processors, desktop publishing, and web browsers. They underlie line wrapping, baseline alignment, leading, and cross-font alignment in multi-font layouts. Accurate typesmetrics facilitate consistent typography across sizes, resolutions, and languages, and are a central concern for font designers, rendering engines, and typesetters.