The Chicago Manual includes extensive information about the use of numbers. Whether to use figures or words depends on the overall style by which you abide and the nature of the material with which you are working.
numbers or words?
Spell out numbers lower than 100 in nonscientific text. If a number higher than 100 is rounded off or approximated, spell it out in nonscientific copy. Otherwise, 100 and higher are numerals, in text. An exception to this is online text, where in a way all bets are off. The idea of online text is to keep it short, with consideration to search engine optimization and other factors that are beyond the scope of print publications. For online writing, numerals frequently are used in all instances. In print or online, for charts and graphs, use numerals. See the Chicago Manual for examples and more information. Treat numbers in the same sentence alike: If there’s a three-figure numeral in the sentence, make all the numbers figures, as long as the figures all relate to the same items.
The students collected 114 books for the sale, 12 of which were first editions.
Having four meetings made it possible for the fifteen committee members to collect 160 used books.
—Ages should be expressed in numerals. (This is University style, not Chicago Manual style.)
I have an 11-year-old daughter and a 10-year-old son.
The student was 35 when he received his doctorate.
However: Dr. Foley celebrated her fortieth birthday.
—Use either a figure or a word—not both: five rooms, not five (5) rooms. Exception: If the information may confusing without both word and numeral to the audience it is meant to reach.
—Use the up-to-100-spelled-out/higher-than-100-numeral rule for ordinal numbers (first, second, forty-fifth, eighty-ninth, 120th, 223rd, etc.). This applies to numbered street names as well: Fifth Avenue, Twenty-third Street.
In street addresses, building numbers are usually written in arabic numerals: 5801 Ellis Avenue. However, when a building’s name is also its address, the number is spelled out: One Park Place.
Always use numerals: 3 credits; 18 credits in history; a 3-credit course; 4 units of English; 1 unit of geometry; 2 units of a foreign language. Also, use numerals when referring to credit hours. (Note use of “in” with credits and “of” with units.)
No apostrophe: 1920s; 1980s; mid-1970s; spell out thirties, forties, fifties, sixties, etc. For those involved in desktop publishing, please note that A.D. and B.C.are set in small caps (typeface about two points smaller than rest of text). If you cannot reproduce small caps on your typewriter, do not worry; the Department of University Publications will make them for you when you submit your manuscript. Also note that B.C. follows the date, while A.D. precedes it.
He was born in 44 B.C.; she was born in A.D. 44.
In some cases, such as edition numbers in reference lists, ordinal numbers are expressed in numerals (4th ed., for example). Unlike the Chicago Manual,University style calls for second and third to be enumerated as shown: 2nd; 3rd.(Chicago Manual calls for 2d; 3d.) Spell out ordinal numbers in straight text: first, seventeenth, twenty-third.
Fractions generally are too cumbersome to spell out and should be expressed in numerals, but judge each case on its own.
The obstacle was a 3 1/2-foot fence.
They had finished about one-third of the course.
In class notes and other text, abbreviate as follows:
Attending the Homecoming reunion were Elise Adams ’64 and John Andrews ’88, ’90g.
Harold Jones ’74 Eng was the first Penn Stater to win the award.
Spell out or use figures according to the general rule (one through ninety-nine spelled out, 100 and higher in numerals). If you spell out the number, then spell out the currency reference and vice versa.
Only if an even dollar amount is in a sentence with a dollar/fraction amount do you use .00 after the amount.
The children paid $1.50 to enter; adults paid $3.00.
If you are preparing a brochure about a conference that has an application fee, use the dollar symbol and numerals. That’s easier for readers to pick out when they’re looking for the cost.
The $75 registration fee covers meals and learning materials.
When referring to something that can be counted, use more than rather thanover.
More than fifty people attended (not Over fifty people attended).
But: Jason is oversix feet tall.
Use a comma for four-digit and larger numbers (except dates): 3,500; 60,000. For very large numbers, use figure and word: 1.2 million, $90 million.
no. and number
Lowercase and use numeral with no. Whether to abbreviate or spell out depends on the nature of the publication. Spell out number in text; abbreviate in listings, charts, or graphs.
Penn State frequently has a number-one football team.
number is or number are
A number are available; the number is specific.
A number of textbooks are on back order.
The number of guests expected is fifty-six.
numbers at the beginning of a sentence
Always spell out numbers at the beginning of a sentence. Rearrange the sentence if spelling out the number makes it cumbersome. Avoid putting numbers next to numbers—separate the numbers with words if possible.
parts of books
Use numerals when you are referring to parts of a book.
Chapter 4; Table 2.5; page 4
Always use numerals; spell out percent in text: 5 percent; 9.2 percent. Use the % symbol in charts, graphs, and scientific and mathematical material.
plurals of spelled-out numbers
Plurals of spelled-out numbers are formed like plurals of other nouns.
quantities as numerals with abbreviations
If a quantity is used with an abbreviation, the quantity always should be expressed in numerals. If a symbol is used with the quantity, use a numeral. For two or more in quantity, the symbol should be repeated:
3″x 5″; 30′ x 50′; 80 km; 2 tsp.
Very large figures should be written as numerals, whether they are approximated or not.
The company distributed more than 1 million books.
The nation’s population neared 2.3 billion.
In mathematical, statistical, technical, or scientific text, use figures. But in ordinary text, treat the numbers according to University style as explained in this section.
times of day
University style supersedes Chicago Manual style on this point. Although times of day are often spelled out in text, in most University material, the time of day is important for scheduling purposes; thus, University style has come to be the figure and a.m. or p.m. in both text and schedule listings. Because time designations are not always on the hour, for consistency, use :00 with times that are on the hour. Note that a.m. and p.m. are not capitalized.
Classes scheduled for 5:00 p.m. and later have been canceled for today.
When possible, drop p.m. or a.m. rather than repeat it.
The meeting will be held from 4:30 to 6:00 p.m.
To avoid confusion, use noon and midnight rather than 12:00 p.m. (noon) and12:00 a.m. (midnight).
I thought he said to meet him at midnight, but he meant that I should meet him at noon.
When preparing a conference agenda, if there are concurrent sessions that begin at the same time but end at different times, list the shorter one first:
10:00–11:00 a.m. Personal Effectiveness
10:00 a.m.–noon Innovations in Higher Education