Style rules for inserting numbers into text vary considerably. Whether numbers should be written out (e.g. two, two hundred) or written as numerals (e.g. 2, 200) depends on what kind of writing is being done.

Numbers as Words

In strictly academic writing, numbers of one or two words should be spelled out with letters. For example: 

• Anthony was able to bike five miles in less than an hour. 

Notice that 5 is written out as "five" because it is one word. 

• Maria bought five bananas, two bunches of grapes, and six oranges for her fruit salad. She needed twenty-one servings for the luncheon.

Notice that each number is written out, including 21, because all of them are one or two words.

Numbers as Numerals

Numbers that are more than two words long should be written as numerals. For example: "Our vacation to North Carolina ended up being 728 miles, as a round trip." Or, in the case of years: "Tony was born in the fall of 1966."

Also, the following numbers are written as numerals:

• Dates: December 7, 1941, 32 BC, AD 1066
• Addresses: 119 Lakewood Lane, 1600 Pennsylvania Avenue
• Percentages: 45 percent or 45%
• Fractions and decimals: 1/3 and 0.25
• Scores: 20 to 13 or 15–18
• Statistics: average age 25
• Surveys: 2 out of 5
• Exact amounts of money: $861.34 or $0.67
• Divisions of books: volume 6 or chapter 5
• Divisions of plays: act 2, scene 4
• Time of day: 12:00 AM or 4:35 PM

Technical Writing

In technical writing (i.e., research writing or other writing that includes measurements or statistics), the proper usage of numbers varies substantially. Typical rules to follow in technical writing include:

• Technical quantities of any amount are expressed in numerals (3 feet, 12 grams, et cetera).
• Nontechnical quantities of fewer than 10 are expressed in words (three people, six whales).
• Nontechnical quantities of 10 or more are expressed in numerals (300 people, 12 whales).
• Approximations are written out as letters (approximately ten thousand people).
• Decimals are expressed in numerals (3.14).
• Decimals of less than one are usually preceded by zero (0.146); however, this may vary depending on the style you are asked to write in.
• Fractions are written out, unless they are linked to technical units (two-thirds of the members, 3 1/2 hp).
• Page numbers and the titles of figures and tables are expressed in numerals.
• Back-to-back numbers are written using both words and numerals (six 3-inch screws).

Special Cases

There are many special cases for writing numbers. A number at the beginning of a sentence should be spelled out as words. Within a sentence, the same unit of measurement should be expressed consistently in either numerals or words. In general, months should not be expressed in terms of numbers.

Numbers in the news

When numbers are used in text, many basic formatting rules apply.