Numbers and Equations in Writing

Numbers in Writing


Arabic numeral/numeral: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

aka: digits, numeral, numerals

Number: represents an amount or size of something that has been approximated, counted, calculated, identified or measured

Quantity: a number that represents a specific measured outcome (example:  4.33 mm)

Ten Baseline Rules

  1. Never begin a sentence with an arabic numeral.  This includes uses for figure captions, headings, subheadings, years, titles, or any other circumstance. Rearrange the use, as needed, to “bury” the numeral behind a word or write out the number.
  2. Spell out simple count under 20. Alternatively, spell out simple count under 10. Choose a method and stick with it throughout the document.
  3. Use numerals for mathematical expressions, calculations, or operations.
  4. Use numerals with units of measurement for reporting data or measurements. Write measurements and data with digits, insert a space,  and conclude with the unit of measurement (example: 83 mm). There are exceptions.  See “Units of Measurement.”
  5. Hyphenate numerals with units of measurement only when they function as adjectives (example: the 3-ft coaxial cable).
  6. Use non-breaking thin spaces to indicate 000s instead of using commas or periods. Do not use the spacebar to insert this type of space.
  7. Include a 0 before the decimal point for fractions (example: 0.41 cm).
  8. Write large approximate numbers with a digit and the word (examples: 76 million; 2 billion).
  9. Use numerals to express ratios. (example: The ratio of bleach to water is 12 to 1.)
  10. Know the conventions of the target audience/publication/organization. There can be slight variations to some of these rules. 

Slide article: Writing Numbers in Technical Documents by Celia Mathew Elliot

Equations in Writing

The inclusion of equations should promote the validity of your work to the audience. Their presence should not slow down comprehension of the material.  To that end, there are certain traditions that have developed around how to format equations in written technical work.

  • You can include short equations inside of a sentence without special formatting or extra spacing. Some publishing venues prefer that you italicize such equations to set them apart from the regular wording of the paragraph.
  • Longer equations should be set apart, outside of the sentence or paragraph. Usually, this is done by creating a blank line, then centering the equation on the next line. After the equation, insert another blank line for readability. See Figure 1, below.
  • After the equation, you should define any symbols, etc. Begin that sentence with the word “where” to signal your reader. See Figure 1, below.
  • If your equation is so long that it breaks onto a second+ line, format it so that the line cuts off before a mathematical sign (+, – =, or x). Then, on the new line, begin with that mathematical sign.
  • Number any equation that will be used again within the written work. This is commonly done by inserting a number in parentheses or square brackets on the right margin. See Figure 1, below.
  • Do not ever let a long equation be split over two pages, if possible.
CHEC: formatting equations

Figure 1: Formatting equations in written work. In general, punctuate an equation as if it was a single word in a sentence. Common practice is to visually isolate the equation, using a blank link before and after the equation, centered.


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