How it works
Size times ratio
Line height is the font size multiplied by a ratio. Leading, the space added between lines, is what the line height adds on top of the font size.
The presets are Tight (1.2), Normal (1.5), Relaxed (1.75) and Loose (2). Type any ratio from 0.8 to 3 and the matching preset lights up, or Custom when none matches.
line height = size × ratio; leading = line height − size
What to copy
CSS gets the unitless ratio, which children inherit as a ratio and so scales with their own font size. The pixel version is there when you need a fixed value, and SwiftUI's lineSpacing takes the leading.
The sample paragraph
The paragraph is set at your size and line height, with every line box ruled, so you can judge the spacing before you ship it.
