Choose a type scale and commit to it

Why this rule exists

Type is the single largest surface of most interfaces; the majority of what users look at is words. Yet designers routinely set sizes by feel, nudging a heading a pixel at a time until it looks about right, and the result is a dozen almost-identical sizes that read as accidental because they are. A type scale is a small, fixed set of sizes with clear jumps between them, chosen once and used everywhere. It gives your typography the thing hierarchy needs most: obvious, repeatable differences the eye can trust. Constraint here is a gift, not a cage, because a limited set of sizes forces genuine decisions about importance instead of endless fiddling. When every size on the screen belongs to one deliberate system, the whole thing feels composed rather than assembled, even when the reader could never name why.