Spell out most whole numbers below 10. Use figures for 10 and above: five, nine, 15, 650. See cross-references below for exceptions to those guidelines. If you're not already doing so, use the number 1 key on your computer keyboard to create the number 1. Don't use the old-fashioned, potentially odd-looking lowercase L key to create the number l.
In amounts more than a million - unless the exact amount is essential - round off to one decimal point. Write out the word million or billion: The grant was for $6.5 million. Always include the words million, billion or trillion when giving ranges: The project could cost $20 million to $25 million, not $20-$25 million.
When numbers must be spelled out, use a hyphen to connect only two-digit numbers twenty-one through ninety-nine. Don't use either a hyphen or the word and when spelling out numbers in the hundreds and thousands: fifty-two, fifty-two thousand, fifty-two million, nineteen fifty-two, one hundred fifty-two students, two thousand fifty-two trips, two thousand two.
Also, spell out ordinal numbers first through ninth when they show sequence in time or place: first base, Third Avenue. Exceptions include county, legislative and congressional districts: She lives in the 2nd District.
Most ordinal numbers 10th and above (21st, 215th and so on) are usually not spelled out. When particular ordinals must be spelled out, use a hyphen to connect two-digit numbers twenty-first through ninety-ninth: twenty-fifth anniversary.
Avoid beginning a sentence with a number. If unavoidable, spell it out. Also, spell out casual expressions: thanks a million, a thousand bucks.
Avoid following the word for a number with a figure in parentheses for the same number. It's redundant. Avoid: The contract will run out in eight (8) days.