13 Numbers and Measurements

The use of numbers and measurements varies across academic disciplines. Some styles require numbers to be spelled out in words while others require numerals. The following guide contains information from OER style guides and disciplinary style manuals on how to approach writing numbers and measurements in your text.

General Rules

1. Spell out numbers from one to nine and use arabic numerals for numbers greater than nine, except as indicated in the checklist below.
2. For ordinals, spell out first through ninth unless they are part of an array that includes a higher ordinal. Ordinals greater than ninth are expressed as numerals unless they occur at the beginning of a sentence (Twelfth-century monks…). Acceptable suffixes are 21st, 32nd, 43rd, 54th.
3. Spell out fractions in running text with a hyphen (e.g., two-thirds).
4. Use commas in numbers greater than 999.
5. For percentages, use arabic numbers and the % symbol. The symbol should be repeated with each number in a range or series (the incidence varied from 1% to 4%; 6% to 7% of cases). If a sentence begins with a percent value, spell out both number and percent.
6. For temperatures, use arabic numerals and the degree symbol (37.8°C).
7. For times of day, use a colon only when a fraction of an hour is indicated (9:05 a.m.; otherwise 2 p.m.). With 12 o’clock, specify noon or midnight.
8. For number ranges in text, use “to” (50 to 100 mg) except for years (1998–99, 1999–2013) and pages (213–223), which take en dashes.
9. For number ranges in tables and parentheses, use an en dash (50–100 mg).
10. Always use numerals with school grades (e.g., Grade 6).
11. Use digits and abbreviations in measurements (e.g., puzzle boxes were 50 cm long, 38 cm wide, and 30 cm tall).

Use numerals rather than words

1. In addresses (Suite 2, 400 West Hastings)
2. For dates (17 May 1948)
3. As designators (day 8, chapter 10, page 9, protocol 5)
4. In figure and table designations (Figure 3, Table 6)
5. For money ($14, $9.97, 6 cents, US$200)
6. For temperatures (20°C)
7. For time of day (11 p.m., 2:45 a.m., 07:30–13:00)
8. With units of measure (2 m, 7.2 kg)
9. With percent symbols (0.02%, 99%)
10. With “million” and “billion” ($1 million, 9.4 billion units)^[1]

Numbers and measurements according to MLA

• Spell out numbers that can be written in a word or two.
• Use numerals when more than two words are needed.
• Use numerals for all numbers that precede units of measurement and to express ratios.
• For consistency, when some numbers need to be written as numerals, make all numbers numerals, even ones that would usually be spelled out.
• Use ordinal numbers (1st, 2nd, 3rd, etc.) for numbered streets and do not format the suffix (-nd, -rd, -th, -st) in superscript.
• Use numerals for fractions presented as decimals
• Spell out a percentage or an amount of money if you can do so in three words or fewer (one percent, thirty-five dollars, etc.)
  • Use numerals with symbols when more than three words would be required ($5.35, $970, 48.5%)
  • Do not combine spelled forms of numbers with symbols
• Use numerals for items in numbered series (chapter 10, page 26, etc.)
• Large numbers may be expressed in a combination of numerals and words (4.5 million)^[2]

Numbers and measurements according to APA

• For spelled out numbers, use full names of units and measurements
• For numerals, use abbreviations and symbols.
• Do not use a period after an abbreviation, except for “inch” (in.)
• Do not make abbreviations plural^[3]

Numbers and measurements according to Chicago

• Chicago’s general rule: spell out numbers zero through one hundred.
  • This includes distances, lengths, areas, and simple fractions.
  • This also includes centuries written out as ordinals (e.g., nineteenth century), though the numeral can be used in this case, as long as it maintains consistency within the text.^[4]