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I was told that numbers under two digits should be written out alphabetically (e.g. one, two, three, four, five, six, seven, eight, nine), and that anything two digits or over should be written out numerically (e.g. 10, 20, 100, 200, 1,400).

Is this best practice, and if so, how come? I feel that it looks better but I'm not quite sure why this is objectively better than writing them all out numerically (e.g. 1, 2, 3, 10, 20, 100 etc.)


marked as duplicate by Andrew Leach, user49727, James Waldby - jwpat7, choster, MrHen Oct 9 '13 at 18:22

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I've used the Chicago Manual of Style. It uses principles rather than absolute numbers. Since it's from memory, I'll gladly make corrections or additions.

  • If it starts a sentence, spell it out. "Nineteen ninety-nine witnessed the return of Star Wars to the big screen." "We saw the debut of Phantom Menace, in costume, in 1999."
  • If it's an approximate number, spell it out. "We closed about twenty issues in the last Sprint."
  • If it's an exact number, use the numerals. "We opened 18 issues last week." "I caught a 9-pound bass." "Elevator capacity: 12 persons."
  • If you start with numerals, keep numerals. If you start by spelling it out, then keep spelling it out. "We have had as few as one and as many as thirty-six employees start in a given month." "We have had as few as 1 and as many as 36 employees start in a given month."
  • Prefer numerals for above 12, but spell out for 12 or less than 12. "Lunch came to six dollars." "Dinner set me back 17 dollars." (But if these two sentences appear in the same document, be consistent and prefer numerals in both.)
  • Scientific descriptions (weights and measures) use numerals. "The human gestation period is 38 weeks." "The rat gestation period is 3 weeks." "The patient was injected with 3 ml of the sample."

The upshot is to use the style guide that your employer or school uses. Or adopt one yourself and use it as your reference.


Part of the answer must be that it’s easier and quicker to write four than it is to write three thousand, nine hundred and thirty-eight. It’s really a matter of personal or corporate style, accompanied by the desirability of consistency. If you write 23, it might look odd to follow it with nine, and if you write 5, it might look odd to follow it with ninety-eight.


This is rather arbitrary, I believe, although there are areas of broad agreement. By which I mean that there are some sources which prefer one style and other that prefer another. If you are writing a newspaper article, your newspaper will no doubt have a style guide that says to do it one way, which may be different from the required style of another newspaper.

That being said, I think that the generally preferred style is as you indicate, i.e. 1 through 9 or 10 should be spelled out, but beyond that it is optional which way you do it. I've also heard it said that single-word numbers should be spelled (e.g. twenty) and multiple word numbers be in digits (e.g. 23).

Here's a couple of sources for style:

As you can see from these, there are certain areas of agreement, but also areas where there are disagreement. One says write out 1 thru 9 with letters, the other says write out 1 thru 10 with letters.

Note that they all say never start a sentence with numerals.

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