The rules for using numbers in academic writing vary among academic disciplines. The conventions described here are for non-technical academic prose where numbers are not a significant focus. Scientific and technical writing will have their own conventions and students should consult a manual dedicated to those standards. The main rules about the use of numbers in standard academic writing are about:
When to write numbers in words
Write in words all numbers under one hundred, rounded numbers and ordinal numbers
For general academic writing, you need to write these numbers in words: all numbers under one hundred (e.g. ninety-nine) rounded numbers (e.g. four hundred, two thousand, six million) and ordinal numbers (e.g. third, twenty-fifth). Exceptions: see below, When to write numbers in digits
The country had been at war for twenty-five years.
Over four hundred soldiers were sent to the war zone.
The thirty-eighth battalion was sent to the war zone for the fourth time.
Write in words numbers beginning a sentence
Either write the number in words or, if that’s awkward, then rewrite the sentence to avoid beginning the sentence with a numeral. Exception: You can begin a sentence with a date.
INCORRECT:130 student volunteers joined the university peace mission.
CORRECT:One hundred and thirty student volunteers joined the university peace mission.
INCORRECT:75 percent of the rental properties were occupied by students.
CORRECT: Students occupied 75 percent of the rental properties in the town.
CORRECT:2008 was a good year to commence university studies.
Write in words approximate numbers and some times of the day
In non-technical academic writing, write in words the number for approximate figures (including fractions) and for full, half and quarter hour times.
- about half the students; a quarter of the university; four times as often; hundreds of times
- six o’clock, half past six, quarter past seven, quarter to nine, midday, midnight
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When to write numbers in digits
|Numbers above 100||Use digits.||I counted 3968 books on the shelves.|
|Money||Use digits for exact amounts but digits and words for rounded and large amounts.||$24.28 (exact amount); 98 dollars; $15 million (rounded and large amounts)|
|Measurements||Use digits with a measurement symbol.||32 °C or 32 degrees centigrade; 6 cm or 6 centimetres|
|Decimals||Give exact amounts in digits.||0.45 not .45; 2.36|
|Surveys||Write survey results in digit form.||A survey of participants revealed that 4 out of 5 students worked.|
|Scores||Write scores in digit form.||Students scored from 8 to 75 out of 100.|
|Statistics||Use digits to describe statistical information.||The survey focused on 90 teachers, 10 principals and 24 auxiliary staff from 20 different schools.|
|Dates||Use this order (day/month/year) consistently.||Tuesday 23 February 2008|
|Spans of numbers||Use digits||pages: 56–74, 115–117; years: 1864–1899, 1998–2008; streets: 36–99 Spa St|
|Divisions in a book||Use digits to refer to divisions in books and plays.||volume 5, chapter 6, page 45; act 2, scene 4|
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When there is a choice between words and digits
In the following situations, there is a degree of choice open to you. In such circumstances, it is of critical importance that you are consistent: choose one format and use it throughout.
|Percentages||Use 55%, 55 percent or fifty-five percent||Over 55% of students passed the examination.|
|Fractions||Write in digits or words. If you use words, join the fraction parts with a hyphen.||¾ or three-quarters|
|Eras (time spans)||Choose from a variety of formats, but be consistent.||the eighteenth century or the 18th century; from the 1960s to the 1990s; during the 2000s; in 2300 BC; in 1770 AD|
|Time of day||Choose from a variety of formats, but be consistent. If you are not using am or pm, then write out the time in words. For midday and midnight, write in words—do not use 12 am and 12 pm.||9 am or 9.00 am or 8.22 pm; the eight-thirty bus; four o’clock in the afternoon|
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How to avoid confusion with numbers in a sentence
Avoid confusion when using two numbers together (run-on numbers) or when dealing with several numbers in a single sentence by:
There were 32 third-grade students participating in the test.
The computer laboratory has 24 thirty-centimetre monitors.
In the region where the 1500 dollar a year support allowance was given for each student’s fees, at least 28 million people lived.
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How to write numbers correctly
There are particular conventions which apply, depending on whether you are required to express numbers using digits or words.
Expressing numbers using digits
- Numbers 1–9999 do not use spaces or commas (e.g. 3333 – no spaces for four-digit numbers).
- Numbers 10 000–999 999 have a single space between the hundreds and thousands (e.g. There were 287 701 participants in the survey.).
- Numbers from 1 000 000 have a single space between millions and thousands, and between thousands and hundreds (e.g. The population of this Australian city was 2 467 789 on the 3 December 2008.).
Expressing numbers using words
- Numbers greater than 999 have a comma after the word thousand and after the word million (e.g. 3 206 411 = three million, two hundred and six thousand, four hundred and eleven).
- Two-digit numbers and fractions use hyphens (e.g. 94 = ninety-four; ¾ = three-quarters).
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Except for a few basic rules, spelling out numbers vs. using figures (also called numerals) is largely a matter of writers' preference. Again, consistency is the key.
Policies and philosophies vary from medium to medium. America's two most influential style and usage guides have different approaches: The Associated Press Stylebook recommends spelling out the numbers zero through nine and using numerals thereafter—until one million is reached. Here are four examples of how to write numbers above 999,999 in AP style: 1 million; 20 million; 20,040,086; 2.7 trillion.
The Chicago Manual of Style recommends spelling out the numbers zero through one hundred and using figures thereafter—except for whole numbers used in combination with hundred, thousand, hundred thousand, million, billion, and beyond (e.g., two hundred; twenty-eight thousand; three hundred thousand; one million). In Chicago style, as opposed to AP style, we would write four hundred, eight thousand, and twenty million with no numerals—but like AP, Chicago style would require numerals for 401; 8,012; and 20,040,086.
This is a complex topic, with many exceptions, and there is no consistency we can rely on among blogs, books, newspapers, and magazines. This chapter will confine itself to rules that all media seem to agree on.
Rule 1. Spell out all numbers beginning a sentence.
Twenty-three hundred sixty-one victims were hospitalized.
Nineteen fifty-six was quite a year.
Note: The Associated Press Stylebook makes an exception for years.
Example:1956 was quite a year.
Rule 2a. Hyphenate all compound numbers from twenty-one through ninety-nine.
Forty-three people were injured in the train wreck.
Twenty-seven of them were hospitalized.
Rule 2b. Hyphenate all written-out fractions.
We recovered about two-thirds of the stolen cash.
One-half is slightly less than five-eighths.
However, do not hyphenate terms like a third or a half.
Rule 3a. With figures of four or more digits, use commas. Count three spaces to the left to place the first comma. Continue placing commas after every three digits. Important: do not include decimal points when doing the counting.
Note: Some choose not to use commas with four-digit numbers, but this practice is not recommended.
Rule 3b. It is not necessary to use a decimal point or a dollar sign when writing out sums of less than a dollar.
Not Advised:He had only $0.60.
He had only sixty cents.
He had only 60 cents.
Rule 3c. Do not add the word "dollars" to figures preceded by a dollar sign.
Incorrect: I have $1,250 dollars in my checking account.
Correct: I have $1,250 in my checking account.
Rule 4a. For clarity, use noon and midnight rather than 12:00 PM and 12:00 AM.
AM and PM are also written A.M. and P.M., a.m. and p.m., and am and pm. Some put a space between the time and AM or PM.
Others write times using no space before AM or PM.
For the top of the hour, some write 9:00 PM, whereas others drop the :00 and write 9 PM (or 9 p.m., 9pm, etc.).
Rule 4b. Using numerals for the time of day has become widely accepted.
The flight leaves at 6:22 a.m.
Please arrive by 12:30 sharp.
However, some writers prefer to spell out the time, particularly when using o'clock.
She takes the four thirty-five train.
The baby wakes up at five o'clock in the morning.
Rule 5. Mixed fractions are often expressed in figures unless they begin a sentence.
We expect a 5 1/2 percent wage increase.
Five and one-half percent was the expected wage increase.
Rule 6. The simplest way to express large numbers is usually best.
Example:twenty-three hundred (simpler than two thousand three hundred)
Large round numbers are often spelled out, but be consistent within a sentence.
Consistent:You can earn from one million to five million dollars.
Inconsistent:You can earn from one million dollars to 5 million dollars.
Inconsistent:You can earn from $1 million to five million dollars.
Rule 7. Write decimals using figures. As a courtesy to readers, many writers put a zero in front of the decimal point.
The plant grew 0.79 inches last year.
The plant grew only 0.07 inches this year.
Rule 8a. When writing out a number of three or more digits, the word and is not necessary. However, use the word and to express any decimal points that may accompany these numbers.
one thousand one hundred fifty-four dollars
one thousand one hundred fifty-four dollars and sixty-one cents
Simpler:eleven hundred fifty-four dollars and sixty-one cents
Rule 8b. When writing out numbers above 999, do not use commas.
Incorrect: one thousand, one hundred fifty-four dollars, and sixty-one cents
Correct: one thousand one hundred fifty-four dollars and sixty-one cents
Rule 9. The following examples are typical when using figures to express dates.
the 30th of June, 1934
June 30, 1934 (no -th necessary)
Rule 10. When spelling out decades, do not capitalize them.
Example:During the eighties and nineties, the U.S. economy grew.
Rule 11. When expressing decades using figures, it is simpler to put an apostrophe before the incomplete numeral and no apostrophe between the number and the s.
Example:During the '80s and '90s, the U.S. economy grew.
Some writers place an apostrophe after the number:
Example:During the 80's and 90's, the U.S. economy grew.
Awkward:During the '80's and '90's, the U.S. economy grew.
Rule 12. You may also express decades in complete numerals. Again, it is cleaner to avoid an apostrophe between the year and the s.
Example:During the 1980s and 1990s, the U.S. economy grew.