Major-third 1.250 stays my default for product UI because it scales without drama Perfect-fourth 1.333 carries marketing pages where the headline must do real work Augmented-fourth 1.414 fits dashboards where six type levels need clear hierarchy Golden ratio 1.618 reads beautiful in editorial but breaks below 14px body Type scale is the quietest decision in a design system and the loudest one at scale. Pick wrong and every component fights you for the next two years. I have shipped four products this year on four different scales, and the pattern is clearer than I expected. Type Scale 1: Major Third (1.250) for Product UI The major third is my default for anything a user touches daily. Body sits at 16px. Caption drops to 12.8px (rounded to 13). H3 lifts to 20px, h2 to 25px, h1 to 31px. That is the entire ladder for most product surfaces, and it works because the steps are small enough that you never feel a jolt between heading levels.…