Line Height
The vertical distance between baselines of consecutive text lines. The single most impactful spacing property for readability, and the one most often set incorrectly.
Line height needs to vary by text size. Headings need tighter line height (1.1 to 1.3) because large text creates too much vertical space at body ratios. Body text needs looser line height (1.5 to 1.8) for comfortable extended reading. The common mistake is applying 1.5 to everything, which makes headings float and body text feel cramped at the wrong size. A typography system defines line height per scale step, not as a global value.
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Related Terms
Letter Spacing
The uniform adjustment of space between all characters in a block of text. Also called tracking. Distinct from kerning, which adjusts space between specific character pairs.
Type Scale
A set of font sizes generated from a consistent mathematical ratio. Instead of picking sizes by feel, you pick a base size and a ratio, and every other size flows from that relationship.