Type scale

A modular type scale derives every font size from a single ratio applied to a base size. The discipline is choosing the ratio for the system's typical surface — UI density, editorial reading, marketing impact — then committing to it across the whole scale rather than per-role.

When to use

• Designing a new typography scale from a base font size and a context (product UI / editorial / marketing).
• Auditing an existing scale where sizes feel off-rhythm or step gaps look inconsistent.
• Extending a scale up or down (e.g. adding a display rung above the existing max).
• Code review: flag hand-picked sizes outside a modular ratio, ratios above 1.5 in product systems, or rems-as-source-of-truth (always derive rem from rounded px, not the other way around).

When NOT to use

• Editorial-only books / long-form prose where the ratio is a typographer's pick and a modular scale would over-constrain. The discipline still applies to documenting the choices, not to forcing a ratio.
• Single-size systems (rare; usually a stopgap during initial system definition).

Canonical preset ratios