In General

The following guidelines apply to the majority of writing except for scientific, statistical, technical, and mathematical writing.

Spell out one to nine. Use numerals for 10 and above.

  • Exceptions: Use numerals for percentages, decimals, credit hours, GPAs, book sections and pages, quantities combining whole numbers and fractions, and when symbols rather than abbreviations are used for units of measure. Also when spelled out numbers are clustered thickly in a sentence or paragraph, it is acceptable to use numerals instead.

We recommend using the word percent in formal running text and the percent sign (%) in tables, charts, scientific and statistical copy, and some informal and promotional copy. Most importantly, be consistent throughout a document.

Use a combination of numerals and words with numbers in the millions and larger.

  • U-M libraries hold more than 8.2 million volumes.

Use a comma for numbers with more than three digits unless they represent SAT scores or years.

  • Estimated undergraduate tuition for Michigan residents in 2006–07 was $9,723.
  • The book, published in 2006, has 1,596 pages.
  • John’s combined SAT score was 1082.

Room Numbers

Campus room numbers should be referred to with the name of the building and the room number, in that order.

  • The Office of Financial Aid is located in the University Center Building, room 1183.


Use numerals with a.m. and p.m. (small caps or lowercase letters) to indicate specific times. For clarity, use noon and midnight in place of 12:00 p.m. and 12:00 a.m. Spell out the hour when using o’clock.

  • The lecture will begin at 10:30 a.m.
  • Professor Stanek will extend her office hours to five o’clock this week.

Years and Decades

In running text, spell out the decade or use the full numeric decade. Use the abbreviated numeric decade format in very informal copy or in lists where space is limited. Do not use an abbreviated format if there could be any confusion about the century. Do not use an ’s in numeric decades (1880s or ’80s, not 1880’s or ’80’s).

  • the eighties
  • the 1880s
  • the ’80s