(Check the GPO Style Manual for a complete treatment of numerals.)
1. Numerals Versus Words
In general, use words for numbers one through nine and numerals for larger numbers.
2. Mixture of Numerals and Words
When a sentence contains 2 or more numbers, and 1 of them is 10 or more, use numerals for each number.
Use numerals for units of measurement, time, or quantity; lists or compilations of statistical data; and nomenclature of programs or hardware.
4. Arabic Versus Roman
Use Arabic rather than Roman numerals except in special circumstances (e.g., pagination of front matter).
5. Ordinal Numbers
Treat ordinal numbers as you would cardinal numbers. Spell out first through ninth. Use numerals beginning with 10th.
Ordinal numbers may be spelled out in titles of formal publications.
6. Repeating Spelled-Out Numbers as Numerals
Except in legal documents, do not repeat spelled-out numbers as a numeral in parentheses.
7. Use of Commas
In numbers of two to four digits, run the numerals together.
In numbers of more than four digits, use a comma between each group of three digits.
NOTE: In some cases, a half space can be inserted instead of commas to avoid confusion when the document may be used in foreign countries.
8. Numbers Nine and Under
Spell out numbers below 10 that do not represent precise measurements or are not grouped for comparison with number 10 and above.
9. Number Beginning a Sentence, Title, or Heading
Spell out any number that begins a sentence, title, or heading.
Rephrase when possible.
10. Common Fractions
Spell out common fractions and approximate values.
11. Round Numbers
Substitute a word for a part of a large number ending in several zeros.
12. Awkward Expressions of Measurements
To avoid awkward expressions of measurement or to save space in tables and figures, add a prefix to the basic unit of measurement.
13. Zero and One
Spell out the numbers zero and one when the words would be easier to understand than the figures or when the words do not appear with numbers of 10 or more.
Use the numerals when the zero and one modify a unit of measurement or time.
14. Numbers 10 and Over
Use a numeral for a single number of 10 or more.
Use numeral for groups of two or more numbers or for related numbers, if any one number is greater than nine.
Use numerals for any numbers, above or below 10, that are followed by units of measurement, time or quantity, or special nomenclature for programs or hardware.
16. Angular Measurement
NOTE: Use the word degree in text or its abbreviation deg for angle and temperature readings in figures and tables; always use the degree sign for latitude/longitude values. You may use the degree sign for temperature when necessary to save space.
17. Chemical Formulas
Use numerals for numbers occurring in chemical formulas and in the names of elements and compounds.
19. Decimal Quantities
Use a zero as a placeholder when a decimal number is between +1 and -1, except when the measurement is in caliber or when expressing a quantity that cannot exceed unity, such as probability.
Fractions standing alone or followed by of a or of an are generally spelled out.
Use numerals for fractions in a unit modifier.
Where possible, change fractions to decimals.
21. Mathematical Expressions
Use numerals for exact sums and prices.
Whole-dollar amounts may be written without added zeros.
23. Names of Programs and Hardware
Follow accepted or specified usage for names of programs and hardware.
Use superscript when possible
24. Page, Reference, Figure, Table, or Section Numbers
Use numerals for numbers in serial designations.
Use numerals for ratios.
Use numerals for scores and points on a scale.
Use numerals to express temperature values.
Use numerals for measurements of time, including clock time.
When using a 24-hour clock, do not add hours, and do not add a colon.