With the many grammatical rules to obey and style guides to choose from, knowing when to spell out numbers can be a little overwhelming. The Internet provides a litany of rules, but it quickly becomes clear that some seem to contradict others, and you're left as confused as when you started.
There are a lot of questions to answer: Is your writing technical and scientific, or more informal? Are rules for online writing more relaxed than novel-writing rules? Which style guide, if any, should you be using?
If you've been avoiding number usage in your writing to dodge this issue, make life easier on yourself by understanding that, while these rules are important, consistency is key.
Even if you go against the grain and choose to overlook the rules, stick to that specific style of literary rebellion and maintain uniformity throughout to avoid your writing appearing childish or amateurish.
Numbers, small to large
A straightforward rule to start off with that's widely accepted by most major style guides is that small numbers, i.e., numbers from one to nine, should be spelled out. And numbers above ten should be written numerically.
- Correct: Studies have found that a daily coffee intake of four cups is a safe amount.
- Incorrect: A new study says kids have their own smartphone by the time they turn twelve.
Remember that numbers ranging from twenty-one to ninety-nine should be hyphenated.
- Example: Football fans rush the field leading to twenty-three arrests.
To avoid confusion and maintain consistency, find the simplest way to express any number. Some stylebooks suggest writing out numbers rather than using numerical figures to avoid readability issues, but large numbers can result in run-on sentences.
- Example: Last month's plumbing bill cost six thousand four hundred seventy-two dollars and twenty-one cents.
While some writers don't like the appearance of numbers in their writing, a simple figure of $6,472.21 might be easier to read, especially if large figures occur frequently throughout the text and space is wasted.
For writers who insist on spelling out numbers, a slightly more simplified way might be better.
- Example: Last month's plumbing bill cost sixty-four hundred seventy-two dollars and twenty-one cents.
Note that numbers above 999 don't require commas to separate written figures.
For large round numbers, it's perfectly fine to spell them out, but consistency should be maintained.
- Correct: This week's lottery prizes range from five million to fifteen million dollars
- Incorrect: This week's lottery prizes range from 5 million to fifteen dollars
- Incorrect: This week's lottery prizes range from five million dollars to $15 million dollars
Starting sentences with numbers
A figure might be the focal point of your sentence, but it should always be spelled out when it's placed at the beginning, regardless of its size.
- Correct: Twenty-four dogs competed in this year's national dog show.
- Incorrect: 24 dogs competed in this year's national dog show.
If you don't want a large number at the beginning of the sentence, you can reword the sentence to aid readability and save valuable space.
- Example: This year's national dog show saw 24 dogs compete to win.
Despite the many nuances surrounding rules, this is one that most writers are consistently strict about. Note that this rule doesn't apply to headlines which you'll often see beginning with numbers, though more so in online writing than in newspapers.
Different style guides maintain a variety of stances on beginning sentences with years, though the Associated Press stylebook allows for it.
- Example: 2020 was a nightmarish year.
Back-to-back numbers
Numbers sitting side-by-side can look a little muddled to the reader, especially considering word and letter spacing can range from book to pamphlet to PDF. To avoid this confusion, always spell out one of the two numbers.
- Correct: We need to find homes for our six 10-week-old puppies
- Incorrect: We need to find homes for our 6 10-week-old puppies
- Incorrect: We need to find homes for our six ten-week-old puppies
Though earlier rules stated to spell out a figure from one to nine, the following example would also work as the primary goal is to avoid confusion and aid readability.
- Example: We need to find homes for our 6 ten-week-old puppies.
Dates, decades, and centuries
Dates can be written one of two ways, depending on the writer's tastes or what style guide they're using.
- Example #1: August 22, 2006 (note that there's no "nd" here)
- Example #2: The 22nd of August, 2006
Either option is fine, though the first is more concisely written, so word economy is prioritized here.
Decades should never be capitalized when they're spelled out.
- Incorrect: The hippie movement of the Sixties and Seventies originated on college campuses in the United States.
An apostrophe goes before the year or incomplete number, and never after. The apostrophe in, say, '60s is there to form a contraction for the numbers being replaced, i.e., "19." An apostrophe should never appear after the figure and before the "s."
- Correct: Some '90s fashion trends are making a comeback this year
- Incorrect: Calvin Harris's song, "Acceptable in the 80's" was a hit in 2007
If you're writing in a more formal tone, it's customary to spell out decades or centuries and avoid the use of apostrophes.
- Example: The fall of the Berlin Wall was held on November 9, 1989 (not the '90s)
Time formats
If you don't want figures popping up in your text when you're describing the time, and you don't feel it's necessary to declare the exact time, you can opt for generic words, like noon, midnight, evening, afternoon, etc.
If the actual time is important to note, then you have a few options to choose from.
- Example #1: The yoga class starts at 6:30 A.M.
- Example #2: My train is departing at 10:37pm
- Example #3: Classes start at exactly 8am
Note the different formats after the time, and that you can leave a space between the time and the AM/PM. It's the writer's choice.
While it's quite common to use numbers when describing times, some writers act on personal preferences and choose to spell them out.
- Example #1: The library closes its doors promptly at six o'clock in the evening.
- Example #2: She was almost late for her two-thirty dentist appointment.
Whole numbers, decimals, and fractions
While it's grammatically correct to write out mixed fractions, many writers prefer to use decimals to avoid confusion. This is similar to the above rule about back-to-back numbers.
- Example: There was a 24 3/4 percent increase in sales of vegan food.
Here, the numbers almost blend together and it's a little unclear. When this number is written out and hyphens are used to separate the numbers, readability becomes sharper.
- Example: There was a 24 and three-quarter percent increase in sales of vegan food.
Clarity and consistency are more important than strictly sticking to rules, so writers often go for a decimal point over fractions.
- Example: There was a 24.75 percent increase in sales of vegan food.
Monetary figures and units of measurement
If a dollar, euro, or pound symbol is used, there's no need to add the word it represents after the figure. While this may seem obvious, it's actually a fairly common error.
- Correct: The Coldplay tickets were pretty pricey at $120.
- Incorrect: The Coldplay tickets were pretty pricey at $120 dollars.
If the price you're mentioning is less than a dollar, or any monetary unit, you don't need to use a dollar sign or decimal point as you write it out.
- Correct: Back in the day, movie tickets were only 99 cents.
- Incorrect: Back in the day, movie tickets were only $0.99.
Again, it's up to each writer to choose what format they want, but many choose clarity for the sake of their readers. You might not like seeing figures or dollar signs in your text, but it reads better than a drawn-out, excessively wordy sentence, like the following.
- Example: My car was totaled last week, and it's going to cost two-thousand seven-hundred and twenty-one dollars to fix.
- Revised: My car was totaled last week, and it's going to cost $2,721 to fix.
Also, units of measurement should always be expressed as numerals.
- Example #1: The greatest weight ever raised by a human being is 6,270 lbs.
- Example #2: One mile is equal to 1.6 km.
When you're dealing with a lot of figures in a range of formats, the process can be admittedly tricky. If you're still struggling, review the major style guides to find one that best suits your writing style.
Without an assigned style guide, you have more freedom. This might sound appealing, but a lack of guidelines can provide too many options to choose from. In this case, simply follow the general rules listed above and remember that consistency and uniformity will ensure your words read as polished and professional.
And if you want to live on the edge and break some of these rules, remember Picasso's famous words: Learn the rules like a pro so you can break them like an artist.