English has many rules for writing numbers, and just as many authorities disagreeing with each other about them. Here are some standard rules that you may want to keep on hand.

Rule: Spell out single-digit whole numbers.

Example: I would like two copies.

Rule: Use numerals for numbers greater than nine.

Example: I would like 12 copies.

Rule: Be consistent within a category. If you choose numerals because one of the numbers is greater than nine, use numerals for all numbers in that category. If you decide to spell out numbers because one of the numbers is a single digit, spell out all numbers in that group.

Examples:

My 11 dogs fought with their 3 dogs.

OR

My eleven dogs fought with their three dogs.

Incorrect: I asked for five books, not 50.

Rule: If you have numbers in different categories, use numerals for one category and spell out the other.

Example: Given the budget constraints, if all 30 science students attend the four plays, then the 7 math students will be able to attend only two plays.

Note that students are represented with figures and plays are represented with words.

Examples:

I asked for 30 pens for my five employees.

I have 10 toes but only one nose.

Try This Little Quiz:

A or B?

1. A. I have 11 dogs and two birds. B. I have eleven dogs and 2 birds.

2. A. We have 26 people in our class. B. We have twenty-six people in our class.

3. A. I need 8 pieces of paper, not twelve. B. I need 8 pieces of paper, not 12.

Answers:

1. A     2. A     3. B

Many people have difficulty knowing when to spell out numbers; this short tutorial offers guidelines to assist with that problem.

Figuring out when to spell out a number can be somewhat confusing at times, and there are differing rules for differing style guides. It’s not as difficult a task as it would seem, however, and some simple rules will aid in knowing when to spell out numbers.

Most style guides state that numbers under 10 must be spelled out. Numbers greater than 10 can be written with numerals. It is pretty clear and straightforward.

But what if your sentence contains numbers over AND under 10? The key here is consistency, as again, most style guides allow for a little “wiggle room.” Either spell out both numbers or use numerals to write both. For example: In a survey, five percent of respondents said they were one hundred percent sure when to write out numbers. The alternative, equally correct version would be: In a survey, 5% of respondents said they were 100% sure when to write out numbers.

Different Rules

There are, however, different rules for scientific writing, where it’s perfectly acceptable to use numerals for all numbers, even those under 10. The style guides for scientific journals often state that, for example, “2” is preferred to “two”—and this makes sense, as you’re dealing with measurements and such.

Generally speaking, in dialog in fiction writing, numbers will be spelled out: He said the restaurant is about eight miles away and we’re to meet him there at one o’clock. Again, an exception to this would be when writing a text message in a work of fiction:  U said 2 b there @ 9, right?

These are basic rules to guide you as to when to spell out numbers; for more precise information, consult the specific style guide you’ll be using when you write.

Originally Posted 10/23/2011 and happily updated 10/26/2017. Thanks for reading!