How to Style Numbers as Physical Dimensions

By Mark Nichol

How to treat numbers in writing in general is a complicated issue dealt with in this DailyWritingTips post and others. The current post focuses on a subcategory of number style: numbers that refer to physical dimensions — an object’s size or the proportion thereof — or to nonphysical scientific measurement.

Occasional, casual references to dimensions are usually best treated by spelling them out (“The footbridge is fifty-four feet long”; “The temperature dropped overnight to twenty-three degrees”). However, numbers in content (generally nonfiction) that frequently details measurements, especially in a technical context, are better displayed in numeral form (“The respective mile-per-gallon performance for the three models is 67, 84, and 53”). In such a case, earlier or subsequent references to the units in question — and, ideally, all measurements — should be styled consistently, even if they otherwise appear in isolation.

Simple fractions (those describing less than a whole, such as one-third) and short mixed fractions (“one and three-eights,” for example) are easily read in word form, but a concentration of fractions is best styled with numerals (“The table is 34 1/2 inches high, 24 inches wide, and 42 1/4 inches long”); again, the form should be consistent throughout a particular piece of content and preferably in a recurring print or online publication.

Abbreviations and symbols for units of measure are always accompanied by numerals and never appear in association with spelled-out numbers; the shorthand is often but not always separated from the numeral by a letter space (consult a style guide about the distinctions).

Also, when unit terms are spelled out with numerals, a dimension used as a phrasal adjective is usually hyphenated before the noun but never after (“a 24-inch waist”; “her waist is 24 inches”), but hyphens are omitted when abbreviations or symbols appear (“a 10 km race”; “a 120 V system”). Note, too, that terms of units of measurement should be abbreviated only when associated with a numeral (“The lightbulbs differed in actual wattage,” not “The lightbulbs differed in W.”)

Number ranges can be indicated by the word to or an en dash (here, as on many Web sites, represented by a hyphen). To is suitable for numerals and spelled-out numbers alike (“The temperature range is 45 to 60 degrees” or “The temperature range is forty-five to sixty degrees”), but the en dash is appropriate only with numerals (“The temperature range is 45-60 degrees”).

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9 Responses to “How to Style Numbers as Physical Dimensions”

  • Sarah Cunningham

    This is a good reminder on how to use numbers. Even tho I learned a long time ago, I can’t remember some of the details. Thanks for the refresher.

  • Debbi

    I learned MANY years ago that one should write out numbers up to nine, but 10 and up may be represented numerically. Is that outdated?

  • thebluebird11

    This whole thing of spelling out numbers just doesn’t sit well with me. I know what the style guides say, but I don’t like it. Obviously there are different style guides, but luckily there are times (and professions) in which you’re not held strictly accountable for adhering to them. In my profession (medical), I see spelled-out numbers as clutter. Also, when you’re looking for a particular number (e.g. a lab result), you’re looking for a NUMBER, not a word. Digits stand out in pages of text, and when speed is an issue, like when you’re poring throught a 500-page chart, it’s so frustrating to have to hunt for things that should be jumping out at you. I would NEVER spell out fractions of any kind: A wound measures 1.2 x 1 x 0.2 cm. A doctor made a 4-1/2 inch incision. A patient might smoke 1-1/2 packs a day, 1-1/2 to 2 packs a day, or possibly 1-2 packs a day. Just give me the numbers and spare me the text! This is made clear by your last example relating to temperatures. If I were looking for a patient’s temperature or if I were on a travel website trying to find out what the average temperature range is in a given area, I would be much more likely to hone in on the exact information if I saw “45-60 degrees” versus “forty-five to sixty degrees.” Text just gets lost amid the other text; the numbers, which have the information I need and am looking for, stand out, and are easier to find.
    Dashes can also help a word or phrase stand out in a sea of text, so it can be advantageous to use them at times that they otherwise might not be called for, if one were playing strictly by style-guide rules. For example, “45-60” stands out more than “45 to 60.” In my field, addding extraneous words (or characters) constitutes “padding the line count,” meaning that you’re adding these unnecessary things in order to get paid more (since we are, unfortunately, paid by the character/line). So when I do editing/proofing and I see someone consistently spelling out numbers or using the word “to” instead of a dash, it gets my hackles up.

  • Mark Nichol

    thebluebird:

    Your arguments are valid. You are a technical editor, whether that phrase is on your business card or not, and you are dealing with technical writing, where numerals, for the reasons you present, are generally preferable.

    The same is true of references works such as encyclopedias, fact books, and travel guides, where features such as “at-a-glance” sections, and even the running text, will style numbers in numeral form for ease of discovery.

    But spelled-out numbers are merited in much writing, including nonfiction, when references to physical dimensions or scientific figures, as well as other amounts, are few and far between.

  • Mark Nichol

    Debbi:

    Your approach is according to the style guide for the Associated Press, followed by many newspapers, magazines, and Web sites; other style guides also recommend that system. However, The Chicago Manual of Style and yet other manuals advocate spelling out numbers up to one hundred, with many other exceptions. Search this site for “style guide” for more information.

  • Mark MacKay

    I’m usually scrambling to meet a deadline when I need number style information. I’ll remember this article. Thanks!

  • Todd

    This raises an additional question for me. I dimly recall that back in the pre-computer era, numbers were often done both ways in Formal writing. For example, “The room contains five (5) air conditioners.”

    My current job requires me to edit technical documents written by other people. Several of our analysts use the text-parenthesis combination shown above, and I always convert it to the rules mentioned on this site. In this example, I delete the “(5)” and leave the “five.” Is this just an archaic style?

  • Mark Nichol

    Todd:

    This redundant format has no place outside of legal documents, and it’s gratuitous in that context, too — a superfluous effort to avoid ambiguity.

  • thebluebird11

    @ Todd and Mark: I too remember coming across the “five (5)” construction, and it does avoid ambiguity, superfluous or not. It is probably more important in handwritten communication, where people might scribble a number, so that a 4 looks like a 9 or a 6 looks like a zero (0), and so on.
    These days, I do see it on prescriptions written by doctors, mainly to avoid the possibility that an underhanded patient will attempt to alter the number of pills prescribed (e.g. from 10 to 40 or 90).
    Actually, it is also required when writing a check; you put in the digits specifying the amount of the check, but must also spell it out in words. However, I have occasionally forgotten to write out the words, and the check will be put through just based on the dollar amount written in digits in the box.
    @ Mark: I guess it’s true that I mainly speak from the point of view of a technical editor. But when I read books, papers, magazines, I am still irked by spelled-out numbers, when digits will do. Luckily I don’t have to write for those kinds of publications! But if I ever do…I know where to look for guidance 🙂

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