10 guidelines for writing numbers and numerals

(Editor’s note: Some of these guidelines are not consistent with AP style, which Ragan.com generally follows.)

How do you express numbers in your writing? When do you use figures (digits) and when do you write out the number in words (letters)? That is, when do you write 9 and when do you write nine?

1. Number versus numeral. First things first, what is the difference between a number and a numeral? A number is an abstract concept, whereas a numeral is a symbol used to express that number. “Three,” “3″ and “III” are all symbols used to express the same number (or the concept of “threeness”). One could say that the difference between a number and its numeral is like the difference between a person and her name.

2. Spell small numbers out. Small numbers, such as whole numbers smaller than 10, should be spelled out. That’s one rule you can count on. If you don’t spell numbers out it will look like you’re sending an instant message, and you want to be more formal than that in your writing.