Spelling Out Numbers vs. Writing Them Using Digits

Professor Eugene Volokh has a good idea:

Spelling Out Numbers vs. Writing Them Using Digits

Eugene Volokh • November 22, 2009 4:48 pm

Any thoughts on what the rule should be here? My sense is that numbers written using digits are much easier to quickly absorb, so I tend to write them that way whenever they refer to something that people might want to use in calculations or comparisons. I’d say, for instance, that “These books tend to sell for 20% below their list price of $8 to $10,” rather than “These books tend to sell for twenty percent below their list price of eight to ten dollars.” But when counting people or things in contexts where the count likely doesn’t need to be grasped as a number suitable for calculation or comparison, I spell out the number, for instance in “There are eight reasons why this law is a bad idea.”