Garner's Guide to Making Briefs More Persuasive: Authority Split on How to Handle Your Numbers
Here's another tip from Bryan A. Garner's The Winning Brief: 100 Tips for Persuasive Briefing in Trial and Appellate Courts. It's a minor point, but when editing a brief you should confirm that the numbers one to ten are spelled out, and numerals (the Arabic digits 0,1,2,3 . . .) are used for all higher numbers. This advice requires breaking Bluebook Rule 6.2 which directs you to, "spell out the numbers zero to ninety-nine in text and zero to nine in footnotes."
Both Garner and the Bluebook make these exceptions to the general rule:
Numbers that begin a sentence should be spelled out.
'Hundred', 'thousand' and other round numbers should be spelled out.
Numerals and spelled out numbers should not be mixed in the same sentence if there are some below and above 10.
Numerals should always be used for briefs which repeatedly refer to percentages or dollar amounts.
Garner also recommends spelling out round numbers of millions or billions, and using numerals for specific numbers. E.g., eight million, but 8,120,000.
The Bluebook also states that only numbers with five or more digits should use commas to separate each series of three digits. E.g., 17,333, but 7333.
Garner wants to ban the use of word-numeral doublets. E.g., three thousand (3,000).