An assortment of metal number forms for a letterpress

Chicago Style Workout 77: Numerals

In Chicago’s default style for numbers, whole numbers under 101 are usually spelled out, as in three or ninety-three. Chicago’s alternative rule spells out numbers up to and including nine. But some expressions always call for numerals (July 2, page 9), and in scientific and technical contexts, numerals (also called digits) are the norm.