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For all numbers, use the Chicago 9.3 alternative rule: spell out single-digit numbers and use numerals for all others except:

  • use numerals in tabular data
  • use numerals when used with the word “percent.” (See Percentages.)

Do say: Olivia Creasey took second place in the 2019 Grad Slam.

Do not say: Olivia Creasey took 2nd place in the 2019 Grad Slam.

Do not use superscript for ordinal numbers.

Do say: The department was ranked 12th in the nation.

Do not say: The department was ranked 12th in the nation.

Numbers in a range

When to spell out the range: This depends on context and the sound of the sentence. There will be times when spelling out a range is more appropriate, and aids in understanding of complex ideas, for example:

Do say: The researchers found that in from 40 to 60 percent of the six-to-eight-cell microtissues assembled with a single abnormal cell …

Do not say: 40-60 percent

Do not say: 6-8 cell microtissues


Use cardinal numbers for dates; do not use ordinal numbers.

Do say: The ceremony will be held on November 14.

Do not say: The ceremony will be held on November 14th.

When abbreviating months or days, use the first three letters and capitalize the first letter.


In formal prose, do use a.m. and p.m. which follows Chicago 9.37 and 10.41 and UCSF Style.

In system fields, lists, and tables, do use am and pm, since our backend scripting language PHP doesn’t have a built-in format for a.m. or p.m. and since it saves space.

Do not use all-numeric dates, e.g., say July 1, 2025 instead of 7/1/2025. This follows Chicago 9.35.

Daylight saving time: If your event occurs on or near a daylight saving time change, call attention to that elsewhere, such as in an event description. Do not specify standard or daylight time.

Time zones:

  1. Do say (formal): “4:45 p.m. (Pacific time).”
  2. Do say (informal): “4:45 pm (Pacific time).”
  3. Include parentheses around the time zone.
  4. Use a lowercase T on “time.”
  5. When referencing central, eastern, or mountain time, use lowercase C, E, and M.
  6. Do not include the word “zone” except in a formal context.
  7. Avoid abbreviations PT, PST, and PDT except it’s okay to use these when the system is managing it.
  8. When multiple dates or times appear on one page, avoid specifying “Pacific time” multiple times. Instead, elsewhere include “All times specified are Pacific time” or similar.


Follow Chicago 9.18: “In nontechnical contexts, the word percent is generally used; in scientific and statistical copy, the symbol % is more common.”

Use numerals with the word percent in most cases, except at beginning of a sentence.

Exception: if the text is dense with percentages (e.g., a detailed research story), or for charts and tables, the % symbol is preferred.

Do say: Only 7 percent of the students replied to the alumni survey. Sixteen percent requested removal from the email list.

Do say: Sixty percent of subjects had full remission, 31.2% had partial remission, and 8% had no response to the treatment (0.8% left the study).

For a range of percentages:

Do say: an approval rating of 40 to 50 percent

Do say: an approval rating of 40% to 50%

Do not say: an approval rating of 40 percent to 50 percent

Do not say: an approval rating of 40-50 percent.

Phone numbers

Do say: 415-476-2577 (included as an option in UCSF Style)

Do not say: 415.476.2577 and (415) 476-2577 and 415/476-2577

Next topic: Punctuation and Spelling