Rules for Writing Numbers

Let's face it, most of us didn't become writers because we're good with numbers. A lot of us are the same people who got straight A's in Literature classes, but struggled to pass Trigonometry. We're writers! We're good with words.

But in many contexts, numbers are words. If you write long enough, you'll have to deal with them eventually. When you do, you might find out--like I did--that you aren't sure how to handle them.

Like many rules, the main thing is to be consistent. Whatever you choose to do about writing numbers, make sure you stick to it.

The most widely accepted stance on writing numbers is that in non-technical writing, you should spell out the numerals. 1 becomes one. 43 becomes forty-three.

But what about 328,747?

When I first went looking for a rule on this subject, I read that you're supposed to write out any number under a hundred. But I found that didn't quite capture it, after all, I'd rather write "a million" than 1,000,000. So there shouldn't be some arbitrary point where you stop spelling out numbers and start writing numerals.

The rule I settled on is that I always write out any number that can be expressed in three words or fewer. 600 becomes six hundred. 47 becomes forty-seven.

That right there is enough to cover most situations, but there are a host of specific types of numbers that have their own rules; time, date, etc. And how do you punctuate numbers? Here is the best, most comprehensive list of number-related rules I can come up with.

  • Write out all numbers that can be expressed in three words or fewer.
    • Nine
    • Twenty-three
    • Eight hundred thousand
  • Hyphenate compound numbers from twenty-one to ninety-nine, even when they are part of a larger number.
    • Thirty-six
    • Three hundred ninety-five (I wouldn't write this number out in fiction, but this example demonstrates the next rule
  • DO NOT hyphenate orders of magnitude like hundred, thousand, or million.
    • WRONG: Two-hundred fifty-two
    • RIGHT: Two hundred fifty-two
  • Using numerals and words combined is acceptable for orders of magnitude one million and higher.
    • 34 million
    • 5.7 billion
  • However, if the number can be easily expressed without numerals, do so.
    • Five billion
    • Six trillion
  • Hyphenate written-out fractions.
    • Two-thirds
    • Three-fifths
  • Write out ordinal numbers, and hyphenate any between twenty-one and ninety-nine.
    • First thing's first.
    • For the thousandth time!
    • Thirty-third place.
  • Always use commas when writing numerals.
    • 1,584,282
    • 2,483
  • But don't use commas when writing out large numbers.
    • WRONG: Six thousand, forty-five
    • RIGHT: Six thousand forty five
  • Always use a zero before a decimal when using numerals. It helps readers catch the decimal point.
    • WRONG: Voter turnout was only .5 percent.
    • RIGHT: Voter turnout was only 0.5 percent.
  • NEVER begin a sentence with a numeral.
    • WRONG: 5,400 people were there.
    • RIGHT: Five thousand four hundred people were there.
    • RIGHT: Fifty-four hundred people were there. (Informal, but preferred, as it condenses the number to three words.)
  • Currency
    • Write out any amount that can be expressed in three words or fewer.
      • Seven dollars
      • Twenty thousand dollars
    • Add a comma between dollars and cents (or between other currencies and their coinage):
      • Nine dollars, twenty-two cents
      • Five pounds, three pence
    • ...unless you're writing it informally
      • A dollar fifty
      • Six and a quarter
    • Do not add the name of the currency when using numerals, use the associated symbol.
      • WRONG: $1,284 dollars
      • RIGHT $1,284
  • Time
    • Write out times that are easily expressed in one word, unless you're being formal.
      • Noon
      • Midnight
      • Nine
      • Six in the morning
    • Use numerals for all other times.
      • 7:30 PM
      • 1:25 AM
      • It is acceptable to drop the :00 for the top of the hour (9 PM), but I don't do it because a) I usually just write out the number and skip the AM/PM, and b) I like the consistent look of having the colon in every time I write.
    • Pick a spelling for AM and PM, and stick with it.
      • AM and PM is the most preferred.
      • A.M. and P.M. 
      • a.m. and p.m. 
      • and am and pm 
      • are all acceptable
    • Put a space between numerals and the AM/PM designation.
      • WRONG: 7:30PM
      • RIGHT: 7:30 PM
  • Date
    • Use numerals for dates when you're stating them formally.  Commas are required in this format.
      • June 30, 2015
      • The 30th of June, 2015
    • Use words when stating them informally.
      • The twentieth is a Friday.
      • He was born March eleventh, right before me.
    • Spell out decades.
      • The sixties
      • The late eighties
    • Use numerals for centuries
      • The 1900s
      • The 2000s
    • DO NOT use apostrophes to pluralize decades or centuries
      • WRONG: The 80's
      • WRONG: The early 1900's
      • RIGHT: The '80s [Do use an apostrophe to stand in for omitted numbers, as I explain in my article on apostrophes]
      • RIGHT: The early 1900s

Any awkward situations I missed? Any rules you disagree with? Drop me a comment!