In nontechnical contexts, the general rule is to spell out one through nine; always spell out one and zero; use numerals for numbers 10 and above.
Whole numbers followed by hundred, thousand, billion, and so forth are usually spelled out:
- one billion
- six million
Spell out general approximations:
- There were enough seats for a thousand guests.
- A million voters can’t be wrong.
Avoid starting a sentence with a number or year, whenever possible. If there is no possible way to recast the sentence, then spell out the number or year that begins a sentence.
When numbers above and below nine occur in the same sentence for similar items, for consistency’s sake they should all be written as numerals:
- At the meeting were 6 CAS alumni, 100 ENG alumni, and 240 COM alumni.
However, items in one category may be given as numbers and those in another spelled out:
- A mixture of buildings—two of 18 stories, five of more than 50, and a dozen of only 3 or 4—are proposed for the area.
Use numerals for all percents, weights and measures, and sports scores.
Use numerals to denote centuries:
- before the 16th century
- 20th-century literature
Use a comma in a number containing four or more digits, except in test scores:
- The freshman class has 4,174 students.
- Her combined SAT score is 1905.
For phone numbers, use a hyphen following the area code:
For 800 numbers, don’t add the 1:
- 800-632-2244, not 1-800-632-2244
In times of day, or dollar amounts, eliminate unnecessary zeros:
- 7–9 pm, not 7:00–9:00 pm
- $45, not $45.00
In ranges of time, dates, dollar amounts, or percentages, use an en dash to denote a range, and it is necessary to use the symbol or abbreviation for only one element of the range:
- noon to 3 pm
The letters in ordinal numbers do not appear as superscripts:
- 122nd, not 122nd
Do not use “rd,” “th,” etc., in dates:
- February 22, not February 22nd
Decades may be written as the ’20s; the twenties; or the 1920s. An apostrophe is incorrect to indicate the plural, so 1920’s is incorrect.