Line-height grid

Line-height in a token-driven system is not a free multiplier — it's a snapped value on the spacing grid. UDTS uses two tracks: lh-ui (tight, for headings / labels / buttons) and lh-prose (loose, for paragraph body). Both derive from the font size and snap to the minor grid unit so adjacent paragraphs and successive lines preserve rhythm.

When to use

• Picking line-height for any font size in a system that has a defined spacing grid.
• Auditing line-heights that "look right but feel off" — usually a sign they're not snapped.
• Setting up a foundation theme that needs both UI and editorial copy on the same grid.
• Code review: flag any unitless line-height (line-height: 1.5) on a system token; replace with a snapped px value from the appropriate track.

When NOT to use

• One-off display elements (hero marketing splashes) where the line-height is hand-tuned by a typographer and the grid doesn't apply.
• Inline contexts where line-height inherits from the parent — the parent owns the grid alignment.

The two-track formulas