This page summarizes a bunch of rules that relate to the use of numbers in academic writing. In general we have followed the guidelines set out by the Modern Language Association (MLA).
The big question with numbers is whether to write them out or use numeric form:
Written out: twenty-two, nine, three million.
Numeric form: 2,000, $45, 99%.
To answer that question you should ask a few more specific questions:
- How many words would it take to write out the number?
- Is the number a specific measurement or statistic?
- How many numbers are you using in a row?
As we answer these questions we’ll see that there are four criteria to consider: length, specificity, frequency, and clarity.
The basic rule is that if you can write out a number in one or two words then there’s no need to use numeric form:
By contrast, numbers that would take three or more words to write out should be written as numerals:
Note that hyphenated numbers between twenty-one and ninety-nine are treated as one word. Also, round numbers higher than a million can be written in a combination of words and numerals:
Dinosaurs are said to have gone extinct 65 million years ago.
Measurements and Statistics
You can break the previous rule if you’re using certain kinds of numbers. These are numbers that are used for specific kinds of measurements, dates, statistics, and so forth. Here are some examples:
Dates and Times:
19 times out of 20
26 Hammock Street
You might think of these numbers as more detailed or technical in character. In such cases you can usually use numerical form.
Again, there are always exceptions. For instance, if it’s easy to express a monetary amount in words you can do so (e.g., three cents, ninety dollars).
The last thing to consider is how many numbers you are using in a particular passage. If you are using quite a few numbers you might use numerals even though the numbers are not technical in nature:
Out of the 23 students, 15 returned the permission slip, 6 forgot and 2 refused to have their parents sign anything for them.
However, this is very much a judgment call. If it’s easy enough to spell out the numbers then do so.
Finally, you can sometimes mix written and numeric form to create clarity:
He made five 3-pointers in a row.
So to sum up what we’ve learned, spell out numbers of one or two words unless the numbers are more specific in nature, you’re using quite a few numbers in a row, or you need to provide clarity.
Starting with a number
Don’t start a sentence with a numeral. Spell it out or change the word order:
Incorrect: 2,000 people rioted in the streets.
Correct: Two thousand people rioted in the streets.
Incorrect: 68% of the population voted in favour.
Correct: It appears that 68% of the population voted in favour.
If you’re dealing with a range of numbers, don’t shorten the second number for numbers under a hundred:
For a range of numbers higher than 100 you should provide at least the last two digits of the second number:
Of course it may often be necessary to provide more information:
You can add some clarity to large numbers by using a comma after every three digits:
However, this rule does not apply to specific numbers such as addresses or dates.
Roman numerals are not used as often as they used to be. For instance, in citing plays, references to act, scene, and line numbers are now generally given in arabic numerals (e.g., 2.3.15-16), though roman numerals are sometimes still allowed.
You will see roman numerals used for the pages of prefaces and prologues. They are also sometimes used to count the pages before proper pagination starts (e.g., pp. v-vii). When you’re dealing with such numerals, don’t change them to arabic form.
Roman numerals are also sometimes used in outlines (though this is not mandatory):
II. The History of Photography
A. The Daguerrotype
In addition, roman numerals are used in some names:
The MLA Handbook (8th ed.) recommends that in citations dates should be given in the format day-month-year:
20 Feb. 1988.
The rationale is that by not using commas you can maximize space. Who knew that one or two commas would be a big deal?
Elsewhere you can use a different format if you like. The main thing is to be consistent. A common way of writing dates is month-day-year:
August 3, 1766
Note that if your sentence keeps going after such a date you’ll have to provide another comma after the year.
The time of day can be given in different ways:
As long as you’re consistent, either of these formulations is acceptable.
Note that if you use the expression o’clock, the number is usually spelled out too (e.g., five o’clock).
Cardinal, Ordinal, and Nominal Numbers
If you’d like to know some of the lingo used to describe numbers, here is a quick rundown.
Cardinal numbers are numbers that are used in counting:
There were twenty children on the bus.
Ordinal numbers are used to describe the rank or position of something in a list:
She was the third runner to cross the finish line.
It’s his fiftieth birthday!
Other examples of ordinal numbers are first, second, fourth, and so on.
Nominal numbers are not used for counting or listing. They are used as names to identify something:
Who wants the number 9 jersey?
Prisoner 2089 is missing.
It can be tricky to tell the difference between cardinal and nominal numbers, as the latter do often involve an element of counting.
If it makes it easier to remember, try this mnemonic (memory aid):
cardinal = counting
ordinal = order
nominal = naming
How Roman Numerals Work
If you have no clue how roman numerals work, here is a quick overview. Let’s start with some basic numbers:
i = 1
ii = 2
iii = 3
v = 5
x = 10
l = 50
c = 100
d = 500
m = 1000
You’ll see these in uppercase or lowercase form.
By combining the numbers you can make other numbers. One way to do so is by placing a smaller number in front of a larger number. The effect is similar to subtraction:
iv = 4 (think 5-1)
xl = 40 (think 50-10)
On the other hand, if you place the smaller number after the larger number then you’re adding the two:
vii = 7 (think 5+2)
lxxxii = 82 (think 50+30+2)
You can also combine these two methods:
xcii = 92 (100-10+2)
There are a few more rules for adding and subtracting, but hopefully this clarifies the basic principles.