Rules for Writing Numbers

Numbers do not only show up in math assignments, but also in everyday writing. Like most things in the English language, there are rules for writing numbers. Yes, imagine that! There are certain numbers that we spell out in letters, while there are others that we only write in numerals (1, 2, 3, etc.). You have probably come across more than your fair share of ‘Top 10’ lists. Why is it not ‘Top Ten’ list? Keep reading to find out.

Numbers That Are Spelled Out

Please note that there are some exceptions to the rules outlined below. As with other grammar rules, rules for writing numbers change according to certain style guides (i.e. Chicago Manual of Style, AP, MLA, etc.). However, here are some general rules for spelling out numbers.

Numbers under 10:

• Martin has two younger sisters and five older brothers. Note: Some style guides recommend spelling out the numbers one to one hundred.

Numbers at the beginning of a sentence: 

• Sixty children came to the class trip last year, but this year there were 80.

Fractions (usually hyphenated):

• About one-third of the class comes from China. Note: However, the exception to this rule is when it is a mixed fraction. We then use numerals (unless it comes at the beginning of a sentence). Example: The recipe calls for 1 ½ cup of nuts.

Numbers That Require Numerals

Numbers 10 and above:

• She has bought about 12 pairs of shoes and 15 dresses in the last three months. Note: However, when numbers are in a list it is best to keep all the numbers in the list consistent, even if numbers are under 10.

Correct: She has four brothers aged 5, 7 12, and 15.

Incorrect: She has four brothers aged seven, nine, 12, and 15.

Dates and Years:

• School begins on August 27, 2009. Note: We do not use ordinal numbers (i.e. 1st, 2nd, 3rd with full dates).

Correct: The play is on March 23, 2010.

Incorrect: April 1st, 2001.

Percentages:

• According to the latest survey there are 52% of teachers who live in the city. Note: However, if a percentage begins a sentence, it should be spelled out. Example: Fifty and one-half percent of students walk to school.

Decimals:

• There was 0.73 inches of rain last month.

More Than One Rule

The following are special cases and are often written in multiple ways.

Decades:

1. She lived in San Francisco in the eighties.
2. During the 1980s she lived in San Francisco.
3. She lived in San Francisco in the ‘80s.

Time:

We usually spell out the time when it is followed by o'clock or when a.m. or p.m. is not mentioned. However, we use numerals when we need to emphasize the exact time and when using A.M. and P.M.

Examples: o'clock

Correct: We have to get up at six o'clock to be on time for school.

Correct: She gets home around eight in the evening.

Incorrect: We have to get up at 6 o'clock to be on time for school.

Examples: a.m., p.m.

1. The accident happened at 8:22 p.m. last night.
2. They did not leave the party until 2 a.m.

We usually spell out noon and midnight instead of writing 12:00 p.m. and 12:00 a.m.

Example:

We came home around midnight and slept until noon the next day.

Large Whole/Round Numbers:

If there are only a few words, we often spell out.

Examples:

1. He earned two million dollars last year. or He earned $2 million dollars last year.
2. Can you loan me twenty dollars?

For larger numbers we write in numeral form ($5, 385, 673)

Final Note

When in doubt about whether to spell out or write numbers, it is best to consult a style guide.

Resources

For a further overview of how to write numbers, you can check out the following sites:

• The OWL at Purdue 
• Grammar Girl
• Daily Writing Tips