Numerals or Words

Do you spell out numbers or use numerals? Chicago Manual of Style recommends consistency, indicating it must sometimes give way to readability. The general rule is that, in nontechnical contexts, spell out whole numbers from one through one hundred, round numbers, and any number beginning a sentence. For exceptions, see Chapter 9. Use numerals for other numbers.

Spell out round numbers (hundreds, thousands, etc.) except in the sciences, whether used exactly or as approximations.