typography
Modular scale
A set of sizes generated by multiplying a base value by a fixed ratio, so every size relates harmoniously to every other instead of being picked ad hoc.
Like a musical scale: pick a base note (say 16px body text) and a ratio (say 1.25), and every other size is some number of steps up or down – 20, 25, 31, 39… The point isn’t the maths, it’s that any two sizes on the page automatically look like they belong to the same family.
Small ratios (1.125–1.25) suit dense, professional interfaces where restraint matters; big ratios (1.414–1.618) suit editorial pages that want drama. The ratio is a design decision, not a law – what matters is having one.