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Writing Numbers in Narrative

March 2006

In the last issue, I discussed the guidelines for forming abbreviations. This issue presents the rules that dictate whether a number should be written out or expressed in numerals. This differs from ordinary writing and technical writing. In *technical* writing you are much more likely to express a number in numerals. The rules listed here are intended mainly as a guide, and apply to writing numbers in narrative rather than in tables.

The Basic Rule When writing numbers in technical narrative
		spell out single-digit numbers (one through nine), and use numerals for multiple-digit numbers (10 and up).
However, again there are exceptions: Always Use Numerals Use numerals when writing
	- specific technical information, such as test results, dimensions, tolerances, temperatures, statistics, and quotations from tabular data, or - any number that precedes a unit of measurement:
		3 mm 7 kg 145 MHz 4 lb
	- a series of both large and small numbers in one paragraph:
		We repaired 22 computers, 8 disk drives, and 14 keyboards.
	- a section, chapter, page, figure (illustration), or table number:
		Chapter 7 Figure 4
	- numbers that contain fractions or decimals:
		7¼ 8.37
	- percentages:
		3% gain 8% sales tax
	- years, dates, and times:
		At 3 p.m. on January 9, 2006 At 15:17 on 20 February 2006
	- sums of money:
		$7 $28.50 $2000 $0.27 (i.e. 27 cents)
	- a person's age.

Always Spell the Number Spell the number when writing
	round numbers that are generalizations:
		about five hundred approximately forty thousand
	fractions that stand alone:
		Repairs were made in less than three-quarters of an hour.
	numbers that start a sentence (or, better, revise the sentence so that it does not start with a number).

Additional Rules There are several additional rules that do not conform to the above guidelines:
	- Insert a zero before the decimal point of any number less than one:
		0.82 0.0035
	- Whenever possible, use decimals rather than fractions
	- Insert spaces or commas in large numbers containing five or more digits:
		4056 27 285 (or 27,285) 3 657 330 (or 3,657,330) (The trend is to replace the comma with a space.)
	- Spell out one of the numbers when two numbers are written consecutively:
		Twenty 50 lb cartons (Do not use a hypen.)
	- Use a dot at mid-letter height (•) to represent that the symbols are multiplied:
		lm•s (= lumen seconds)
	- Always as a symbol when a number is used with measurement unit, but always spelled out when no number is used with the unit:
		The tank holds 450 L. (Capacity is measured in litres.)
	- Add a space between the last numeral and the first letter of the symbol:
		354 mV 27 km 121.5 MHz
	- Do not use spaces within the measurement unit:
		3.5 kg 150 mm 18.6 kPa

I continue to receive encouraging comments about the topics presented. If you have any questions about a particular aspect of writing, please email me at LisaM@rgilearning.com and I can address it in a future article.

Online instruction on how to write effective reports and proposals is available at www.rgilearning.com
© 2006, RGI Learning

Lisa Moretto is the President of RGI Learning, Inc. For 15 years she has helped engineers improve their oral and written communication skills. Visit www.rgilearning.com or call (585) 461-3617 to learn about RGI's courses.

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