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
- When to write numbers in digits
- When there is a choice between words and digits
- How to avoid confusion with numbers in a sentence
- How to write numbers correctly
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
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
|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|
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|
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.
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).