Number Rules

Numbers that can be written as one or two words should be spelled out:

Examples:

  • There were seventeen students in class today.
  • The professor told us that fifty-six students were to participate in the experiment.

Other numbers, including fractions and decimals, can be represented as numerals:

Examples:

  • Over 101 dogs were found abandoned at the residence.
  • The book had nearly 1,100 pages of text—far too many to read in one week.
  • We expect a 5½ percent wage increase next year.
  • The plant grew 0.79 inches during the week.
  • If any number begins a sentence, it should be spelled out:

Example:

  • Five thousand years ago, the English language would be barely recognizable to us now.

Use numerals when they proceed units of measure:

Examples:

  • The experiment measured 16 amperes.
  • I filled the flask with 5 milliliters.
  • I weighed 200 pounds at the beginning of the competition.

For large numbers, use a sensible combination of numerals and words:

Example:

  • Looking 9.8 billion years into the past requires a powerful telescope.

Express related numbers in the same style:

Examples:

  • Only 5 of 250 delegates showed up for the convention.
  • You can earn from five hundred to five million dollars in this venture.

When referring to page numbers in text, use numerals:

Example:

  • I referred to page 75 of my textbook when I needed help.
Other special cases
Examples
Spell out centuries in lower case: The twentieth century was a violent time.
Hyphenate centuries used as adjectives: I love nineteenth- and twentieth-century literature.
Be consistent. Use lowercase if spelled out: The nineties (or, the 1990s) were a crazy decade for me.
BC abbreviation follows the year: Our investigation lead us all the way back to 19 BC.
AD abbreviation comes before the year: The Roman Empire was already in decline by AD 500.
Use a numeral for standard times: At 2:00 p.m., we’ll meet for lunch.
Spell time out when using “o’clock”: At five o’clock, the race began.
Use numerals for scores, along with an en-dash: The Knicks won 97 – 88.