Numbers

A. You’re right. Numerals are shorter than words, and they are arguably easier to read. Plus, an all-numeral style would make an editor’s job easier. But the digits in a number like 7 imply a precision that’s usually reserved for the sciences and other technical contexts. Even in the sciences, numbers in the form of ordinals are often spelled out below 10th, on the principle that an ordinal refers to a ranking rather than to a precise quantity.

On the other hand, numerals are customary in certain contexts even in the most literary of prose. In Chicago and most other styles, for example, you’d use digits to refer to page 3 or page 115, a bulb of 40 watts (or 450 lumens), and a 3 percent raise issued on February 1. But aside from these and (pun alert) a number of similar exceptions, words are still Chicago style below 101 in nontechnical settings and below 10 in journalism and technical (but not purely scientific) contexts (see CMOS 9.2 and 9.3).

You can blame the persistence of spelled-out smaller numbers outside the sciences on a combination of tradition and reader expectations, two (not 2) factors that tend to reinforce each other.

A. AP style makes sense for reporters, who often need to achieve clarity in the fewest possible words. And for those of us who haven’t memorized the chronological sequence of NFL championship games, “1969 Super Bowl” is more meaningful than “Super Bowl III.” However, both are correct, and you can use the latter when you’re not following AP style. As for the number, you could always refer to “the third Super Bowl,” but to reflect how the game is generally known, you wouldn’t write “Super Bowl 3”—in spite of what AP might say—any more than you would describe Joe Namath (the winning quarterback in that contest) as having worn number XII (or even number twelve) on his jersey. In other words, it’s Super Bowl III (and number 12).

A. Chicago’s alternative rule for spelling out numbers, like the general rule, applies equally to cardinals and ordinals. If you’re following the general rule (and spelling out zero through one hundred), you would refer to the seventh and seventeenth centuries; for the alternative rule (zero through nine), you would refer to the seventh and 17th centuries. That approach works for occasional references to either or both centuries. But if you need to refer often to both one- and two-digit ordinals in the same context, you can use digits for all of them for the sake of local consistency (e.g., “the 7th and 17th centuries”). See also CMOS 9.7.

A. CMOS normally spells out numbers up to one hundred, cardinals and ordinals alike (i.e., “five” and “fifth”; “eighteen” and “eighteenth”). But we recognize that in some contexts numerals are preferred (e.g., “page 5” and “5th ed.”). If that’s the case in golf, you have our permission to comply. But consider also the advantages of referring to, for example, a “par 4 fifth hole,” where a mix of numerals and words might be helpful. And note that the fabled nineteenth hole is often so spelled. Whatever you decide, let consistency and clarity be your guide.

A. That example in chapter 8 is intended only to illustrate that when a decade or century is written in words, such an expression isn’t capitalized. Our usual preference would be for numerals (“1800s”), but either form is acceptable (choose one and be consistent). Note that Chicago considers “1800s” to be equivalent to “nineteenth century”—which also happens to be the more common way of expressing a century in words. (Under Chicago’s alternative rule for numbers, according to which numerals are used for numbers greater than nine, it would be “19th century”; see CMOS 9.3.) We should also note that in Chicago style, “1800s” and “1900s” refer to the whole century, not just the first decade. For more, see our post on decades at CMOS Shop Talk.

A. Consistency isn’t always a realistic goal with numbers. For example, no one would write a sentence like this one: “We counted 5.3 million fish in the year 2 thousand, but somehow I managed to catch only 3.4 tens.” In your example, “470 thousand” would be almost as intelligible as “470,000,” but the usual convention is to reserve a mix of words and numerals for millions and above—a cutoff designed to prevent strings of digits that are longer than their verbal counterparts would be (see CMOS 9.8).

A. We get this question a lot. Let’s start with the conventional formats—July 24, 2020 (typical US style); 24 July 2020 (typical style outside the US); 2020-07-24 (ISO style). Each of these uses a cardinal rather than an ordinal numeral for the day, whether the year is expressed or not (i.e., July 24 or 24 July, not July 24th or 24th July). Outside of these conventional formats, our recommendation would be to spell out ordinals for the day of the week even when the month is mentioned: the twenty-fourth of July; the twenty-fourth (but the Fourth of July or the Fourth for the US holiday; see CMOS 8.89). But keep in mind that this rule applies primarily to formal, long-form prose—so it’s possibly a little too formal for many contexts; if you prefer numerals, or if you need to use them to save space, you have our blessing (the 24th of July, or the 24th). And if you follow Chicago’s alternative system of spelling out only one through nine, an all-numeral approach for days will facilitate consistency (e.g., we’ll be offering tours on the 1st, 2nd, and 24th of July).

A. Decimal quantities are considered to be plural; quantities expressed as fractions are considered to be singular. So write “0.8 miles” but “eight tenths of a mile.” For decimal forms, only the number one is singular: 1 mile. Once you add a decimal, even if it’s a zero, it becomes plural: 1.0 miles. See CMOS 9.19.

A. According to CMOS 9.4,“The whole numbers one through one hundred followed by hundred, thousand, or hundred thousand are usually spelled out.” The spelled-out form “fifteen hundred” qualifies. But the hybrid form “one thousand five hundred” does not. Paragraph 9.4 is intended to encourage spelling out round numbers like three hundred thousand, not awkward forms like “three hundred thousand six hundred”—or, for that matter, something like “thirty-three hundred thousand,” which would be better expressed as “3.3 million” (see CMOS 9.8). So write “fifteen hundred” or “1,500,” depending on context. (For example, if numerals are otherwise rare in your text, opt for the former.)

A. When expressing binary bit strings (or any specific numeric component thereof), it makes sense to use numerals: e.g., 11111100011 (binary for 2019). But when discussing binary numbers as a concept—as in your example—you can refer to zeros and ones as the basis of the system. This has the advantage, among others, of avoiding the plural forms 1s and 0s (which in some fonts will look almost like words).