Appendix B: Writing Numbers

Professional communicators have a few points of debate in how to write numbers, but most of the advice is pretty consistent.

Here are the numbers that are virtually always written as words: zero, one, two, three, four, five, six, seven, eight, and nine.

There is some disagreement about ten/10, so go with the style used in your industry or by your employer. For myself, I use “10” unless there’s some reason to do otherwise. (In academia, APA recommends “10,” but MLA recommends “ten,” so there’s no one right answer there, either.)

Numbers greater than 10 are written as digits until you reach the millions. Then, for ease of reading, you may write large numbers in the following style: 3.2 million, half a billion, 453 billion, 1.22 trillion, and so on.

When writing a number less than one and greater than -1 in a decimal format, include a leading zero before the decimal point. That is, write “0.5” and not “.5” or “-0.25″ and not -.25”; this will provide greater visual clarity.

Negative numbers are always written as digits, showing the negative symbol before the number.

If your number has units attached or is expressed as a fraction or in some mathematical equation, always express it as digits. Here are some examples: $1.00, 2%, 3/4, 5°, and so on.

With percentages, you should usually use the percent symbol, but writing “percent” is also acceptable. Whatever choice you make, be consistent. Do not write “per cent” with a space in it.

Avoid using apostrophes with numbers in professional writing. If you must use them, remember that the rules of apostrophes apply equally to numbers and words. They show possession or missing numbers. They do not indicate plurals (but plurals can have possession). Here are examples with explanations.

Right: When you’re abbreviating a decade: I loved the music of the ’60s so much! What that means is that I loved the music produced from 1960 through 1969. 
Wrong:  I loved the music of the 60’s so much! This is wrong because “so much” doesn’t belong to the decade of 1960-69. The word isn’t possessive. The apostrophe shows letters being omitted there.
Right: When you’re showing possession: For me, 1960s’ music is the best! This is probably what the person means; they like the music produced from 1960 through 1969, not only one particular year. With plural possessives, the apostrophe lands after the “s” showing a plural.
Probably not: For me, 1960’s music is the best! This means that the person likes the music from only the year 1960, not the whole decade. They probably don’t mean to say this.
Awkward: For me, ’60s’ music is the best! This is technically acceptable, but ugly and confusing. Avoid this treatment.
Right: When showing a plural only: The 1960s was a decade of exceptional music. The writer is simply discussing the decade as a whole. There is no possession and there is no abbreviation. No apostrophe is needed.
Wrong:   The 1960’s was a decade of exceptional music. There is no possession. Delete the apostrophe.

Numbers with more than three digits have a comma every third digit, counting from right to left. Here are some examples: 1,234; 56,789; 123,456. There are a few exceptions, such as calendar years. If writing that “1999 was the best year in the history of cinema,” don’t add a comma in the year. If you’re writing about ancient history or the distant future, you should include the comma for years of 10,000 or larger, such as “25,000 BCE.”

Do not add unnecessary spaces where commas would be clearer.

International note #1: in much of the world, the usage of commas to separate large numbers and the use of periods to separate whole numbers from decimals is reversed. For example, in Switzerland, what is written as “$12,345.68” in North America would be written as “$12.345,68″ instead. Keep your eyes open for this difference in style.

International note #2: if you were educated in India, you may be used to including a comma between the third and fourth digits (counting from right to left), and then a comma every other digit after that (continuing from right to left). This is unique to India. This comma pattern aligns with a “lakh” (100,000) and a “crore” (10,000,000), which are numerical groupings popular in India, but not elsewhere. In India, a lakh is written as “1,00,000” and a crore is written as “1,00,00,000.” India is an outlier in this regard. Most people do not recognize or understand this comma placement. Use standard comma placement outside of India.

Of course, there are some exceptions.

If you’re beginning a sentence with a number, you’ll write out the whole number to avoid confusion. Here’s an example: “Fifty-five years ago, music reached it’s zenith.”

If you’re keeping score at a sporting event or putting a number on the back of a player’s jersey, the numbers are always expressed as digits. Addresses are virtually always expressed as digits, even when only a single digit is part of the address, and commas are not added in street numbers of four digits or longer.

These are the standard practices in professional documents. If your employer or industry deviate from the above advice, then you should deviate in keeping with that pattern, but be consistent in your treatment of numbers within each document you produce.



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