The general rule I follow is to spell out numbers < 10. Also when use numbers before measurement I don't spell out.

For example:

  1. I bought nine apples
  2. We need 5 mL acid for this reaction

How about numbers before "days", "months" and "times"?

  1. Jack, you already did it three times!
  2. It has been five months since she left me.

Is spelling out better?

  • 2
    Welcome to Writing. Are you asking specifically in the context of technical writing? I ask because that's how you tagged it but your examples don't look like tech writing. Feb 21, 2019 at 16:17
  • 1
    Hi Monica. It's tech writing. Example: the animals were treated three times a week for ten weeks. Feb 21, 2019 at 17:49

2 Answers 2


This depends on your style guide. If you're following APA, all of your examples look good to me. My reasoning:

  1. I bought nine apples: The number is under 10 and no special rules apply.
  2. We need 5 mL acid for this reaction: It is written before a "unit of measurement", so it is written as a number.
  1. Jack, you already did it three times!: The number is under 10 and no special rules apply.
  2. It has been five months since she left me: This looks like an "approximate unit[] of time", so it's written as a word.

Here's what APA says:

Use numbers to express the following:

  • numbers 10 and above. Examples: 12 cm, the remaining 10%, 25 years old
  • numbers in the abstract of a paper or in a graphical display within a paper
  • numbers that immediately precede a unit of measurement. Examples: a 5-mg dose, with 10.54 cm of
  • numbers that represent statistical or mathematical functions, fractional or decimal quantities, percentages, ratios, and percentiles and quartiles. Examples: multiplied by 5, 3 times as many, more than 5% of the sample, a ratio of 16:1, the 5th percentile
  • numbers that represent time, dates, ages, scores and points on a scale, exact sums of money, and numerals as numerals. Examples: 1 hr, 34 min, 2-year-olds, scored 4 on a 7-point scale. Exception: use words for approximations of numbers of days, months and years. Example: about three months ago.
  • numbers that denote a specific place in a numbered series, parts of books and tables, and each number in a list of four or more numbers. Examples: Grade 8 (but the eighth grade), Table 3, Row 5.

Use words to express the following:

  • numbers zero through nine in the text (except as described above).
  • any number that begins a sentence, title, or text heading (when possible, reword the sentence to avoid beginning with a number). Example: Thirty-three percent of the sample were men.
  • common fractions. Example: one fifth of the class, two-thirds majority
  • universally accepted usage. Examples: The Twelve Apostles, Five Pillars of Islam.

From the APA 7th Edition Referencing Guide. The 6th edition was pretty much the same in this regard.

Note: The APA Blog clarifies that for "approximate units of time" you should use words.

For the sake of completeness, I found 14 (or Fourteen) Rules for Writing Numbers in Fiction. The rules are different than for a technical writing style guide like APA.


I honestly think it is a matter of flow. Spelling out numbers is more intended for an audience you expect to read what you are writing whereas writing out the numeric forms is more for skimming. At least I have noticed that it is easier to skim through a passage that has numerals in it. They stand out among regular letters, and make them seem more important than the rest.

"Three days later." looks better than "3 days later." There is something about numerals that starts to seem rather like you are reading someone's chat message. If this is text on a note that a character is reading, the second option makes sense. Numerals for dates -such as years- makes more sense as they are much more laborious to read when written out, and can tend to take away from the flow of the story. "It was in 2018." reads better than "It was in two thousand eighteen." The numerals also give more indication of what is being spoken of. The second option could just as easily have been a reference to the amount that something had originated from.

In the same vein I agree with you that measurements make more sense as numerals than as written words because the number measurement is frequently followed by a letter based indication. With two letter indications for measurement one can get lost in the other as the reader moves through the text. "I filled the cup 5 ml." does not get lost as easily as "I filled the cup five ml."

I hope this take on it helps you.

  • 1
    interesting though, if you are quoting, 2018 does not control how the character says it. "it was twenty-eighteen" vs "it was two thousand eighteen" has different tone.
    – Andrey
    Feb 21, 2019 at 18:55

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