Baseline grid
Noun. A typographic ruling of horizontal lines spaced at the body-text line-height interval, used to align every text line on a page so that body, captions, headings, and sidebars all share a unified vertical rhythm.
Origin
The baseline grid descends directly from letterpress. Type was cast on metal bodies of fixed height (the point size); when set, every line was separated by lead spacers (the leading). The result was rigid baseline rhythm enforced by physics. Modern phototypesetting and digital typography removed the constraint, but the visual effect remains a hallmark of professional work — Jan Tschichold (The New Typography, 1928) and Robert Bringhurst (The Elements of Typographic Style, 1992) both argue strongly for baseline rhythm as a core typographic discipline.
Standard value
Baseline interval = body-text line-height. For 16px body × 1.5 line-height, baseline = 24px. Headings and other elements use line-heights that are integer multiples of the baseline (24, 48, 72) so they snap to the same grid.
On the web
CSS doesn't expose true font-baseline metrics directly, so web baseline alignment is approximated through consistent unitless line-heights and matching margins. Editorial frameworks (Compass Vertical Rhythm, Tailwind's leading scale) make this manageable.
Why baseline rhythm matters perceptually
The eye returning to the start of the next line after finishing the current one is a small involuntary motor task that the reader performs hundreds of times in a long-form article. When consecutive lines sit at predictable vertical positions, this return-sweep is automatic; when line positions drift unpredictably, the eye has to search slightly for each next line and the cumulative cognitive load slows reading. Readers rarely notice the effect consciously but it shows up in measurable reading-speed studies. Baseline rhythm is the cheap typographic discipline that delivers the most measurable usability benefit per unit of designer effort.
When to relax baseline discipline
Marketing pages with minimal prose, hero sections with display type, and image-heavy layouts have so little continuous reading that strict baseline alignment provides little perceptual benefit. In these contexts the visual rhythm of asymmetric placement and varied spacing matters more than text-line predictability. The rule of thumb: enforce baseline rhythm in regions with more than ~50 words of continuous prose; relax it elsewhere.