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:

  • 617-353-9253

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
  • $25–50
  • 75–80%

The letters in ordinal numbers do not appear as superscripts:

  • 122nd, not 122nd

In writing dates, do not use “rd,” “th,” etc.:

  • 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.