Numerical information should be conveyed in such a way as to be understood quickly, easily and without ambiguity. For this reason, numerals are preferred to spelled-out forms in technical writing. Except in certain adjectival expressions (see 5.05 Adjectival expressions and juxtaposed numbers) and in technical writing, write out one-digit numbers and use numerals for the rest. Ordinals should be treated in the same way as cardinal numbers, e.g. seven and seventh, 101 and 101st.
Many other factors enter into the decision whether to write numbers out or to express them in numerals. This chapter discusses the most important of these and presents some of the conventions governing the use of special signs and symbols with numerals. The rules stated should, in most cases, be regarded as guidelines for general use that may be superseded by the requirements of particular applications.
Write out numbers used figuratively:
Numbers in the millions or higher should be written as a combination of words and figures:
When such compound numbers are used adjectivally, insert hyphens between the components (see 5.05 Adjectival expressions and juxtaposed numbers):
Whether or not it is used adjectivally, the entire number (numeral and word) should appear on the same line.
Numbers with a long succession of zeros should normally be rewritten. Thus 2.6 million is preferable to 2 600 000.
Numbers are normally rounded to no more than three significant digits. Thus 2 653 000 becomes 2.65 million, not 2.653 million.
The proper form for large numbers that must be written in full is as illustrated:
The practice of writing a number in full and then repeating it in numerals in parentheses should be reserved for legal documents:
Numbers modifying the same or similar items should be treated alike within a given passage. If numerals are to be used for any, they should be used for all:
Where many numbers occur in close succession, as in scientific, technical or financial documents, express all of them in numerals.
Spell out a number—or the word number—when it occurs at the beginning of a sentence, as well as any related numbers that closely follow it:
Where this would result in a cumbersome construction, recast the sentence. The first sentence above could be rewritten as
To avoid starting with a number, it may be possible to end the preceding sentence with a semicolon or to punctuate in some other manner. Instead of writing
you could insert a semicolon after past or write ". . . in the past, and 1994 . . . ."
In accordance with 5.10 Quantities and measures, a number followed by a unit of measurement may have to be written in numerals. Thus, to avoid using numerals at the start of a sentence, rewrite
Normally, for numbers used in adjectival expressions, follow the rule given in 5.01 Introduction, i.e. write out those from one to nine and use numerals for the rest:
If the unit is represented by an abbreviation or symbol, use numerals (see 1.23 The International System of Units (SI)):
Do not use a hyphen between a numeral and a non-letter symbol:
When a number immediately precedes a compound modifier containing another number, spell out the first or the smaller number:
Use numerals for numbers treated as nouns in mathematical usage:
Algebraic expressions used in association with units of measurement should be distinguished from the latter by means of italics, unless the units are written in full:
The usual forms are:
Certain types of ratios may be re-expressed as percentages or decimals. For example, a slope of 1:10 (or a slope of 1 in 10) may be written as a 10% slope.
In non-technical writing, spell out simple fractions, especially when used in isolation:
When a fraction is used adjectivally, place a hyphen between the numerator and the denominator unless either of these elements is itself hyphenated:
Fractions such as the last two, which lend themselves to confusion, are better expressed in numerals.
For the use of hyphens with fractions, see 2.11 Fractions.
It is incorrect to use th or ths after fractions expressed in numerals:
A fraction expressed in numerals should not be followed by of a or of an:
If the sentence seems to require of a, the fraction should be spelled out.
Mixed numbers (combinations of a whole number and a fraction) should be given in numerals:
In technical and statistical writing and with SI/metric units, decimals are preferred to fractions. Normally, no number should begin or end with a decimal point. A zero is written before the decimal point of numbers smaller than 1, while in whole numbers the decimal point should either be dropped or be followed by a zero:
See also 5.16 Market quotations.
Zeros may be used to indicate the number of decimal places to which a value is significant: 0.60 implies significance to two decimal places, 0.600 to three.
In many countries the decimal marker is the comma, not the period. In Canada, however, the period is the generally used decimal marker in English-language texts.
The Canadian Metric Practice Guide (CAN/CSA-Z234.1-89) of the Canadian Standards Association specifies that groups of three numerals (triads) shall be separated by a space, except in the case of monetary values. It advises against the use of commas as separators. Although both commas and spaces are still widely used in Canada, The Canadian Style recommends that, except in financial documents, a space be used instead of a comma. Such a space is also to be inserted after groups of three digits to the right of a decimal point. Note that numbers of four digits only (on either side of the decimal marker) need not be so spaced unless used in combination with other numbers of more than four digits. The following examples illustrate the correct use of the space to separate triads of numbers:
|5005 or 5 005||5.0005 or 5.000 5|
|50 005||5.000 05|
|500 005||5.000 005|
|500 005 000||5.000 005 000|
Omit the space in pagination, inclusive numbers, addresses, numbering of verse, telephone numbers, library numbers, serial numbers and the like.
(a) When quantities or measures consist of two or more elements, when they are used in a technical context, or when a decimal marker is involved, write them in numerals. Otherwise, follow the rule of writing the number out if it is less than 10 (see 5.01 Introduction):
(b) Use of the International System of units (SI) is now the norm in technical writing. Basic information about SI symbols and their use is found in Chapter 1 Abbreviations of this guide. For more detailed information, consult the Canadian Metric Practice Guide.
As noted in 1.23 The International System of Units (SI), SI usage requires either that both the number and the unit be written in full or that both be abbreviated:
Prefixed units should not normally appear as denominators in expressions of the form g/cm3, which should be re-expressed in terms of cubic metres. An exception to this rule is the symbol kg, since the kilogram is considered the base unit of mass.
(c) When one type of unit is converted to another in non-technical work, the converted value should normally be rounded to within five percent of the initial numeral and should be preceded by the word about or some other indication that the value is an approximation:
(d) Note the following conventions for using the degree symbol:
See 1.17 Number and percentage symbols for use of the term percent and the percent sign.
Sums of money are usually expressed in numerals, except when they refer to round or indefinite amounts or are used in a formal or legal context:
Use the following forms:
The abbreviations B for billion, M for million and K for thousand are often encountered, especially in newspaper headlines. Avoid them in formal writing. Note that there is no space between the numeral and the letter:
When dollar amounts are used with SI symbols, the following forms are required:
Place the dollar sign before the numeral in question.
For representation of dollar amounts in Canadian and other currencies, see 5.26 Other considerations.
Except in descriptive text and in approximations, write the time of day in numerical form:
In a scientific or technical context, express precise measurements of elapsed time by means of the internationally recognized symbols of time d for day, h for hour, min for minute and s for second:
These symbols should also be used when units of time are expressed with SI units:
In documents presented in both official languages, and in all forms of international communication, it may be desirable to use the 24-hour system for representing time of day, in accordance with International Standard ISO 3307 and the Treasury Board Federal Identity Program Manual.
The hour is represented by a two-digit number ranging from 00 up to 23 (or 24), the minute and second are represented by a two-digit number ranging from 00 up to 59, and the colon is used as a separator between hour and minute and between minute and second, as illustrated:
|with seconds||without seconds|
The instant of midnight should be represented (when seconds are included) as either 24:00:00, the end of one day, or 00:00:00, the beginning of the next day, according to circumstances.
For calendar dates, the common alphanumeric method remains acceptable, provided that cardinal numbers are used:
When the day and month only are given, cardinal or ordinal forms may be used:
Note also the usage
For the use of the comma in dates, see 7.20 Dates, geographical names and addresses.
The all-numeric form of dating may be more appropriate for such purposes as office memorandums and chronological files and on documents such as certificates, forms and plaques that are presented in both official languages. The format prescribed below is in accordance with the Treasury Board Federal Identity Program Manual, National Standard of Canada CAN/CSA-Z234.4-87 and International Standard ISO 2014. The year, month and day should be separated by a space or hyphen, as illustrated:
The advantage of international standardization in this format is that, whereas 2/06/95 could mean either June 2, 1995 or February 6, 1995, the form 1995-06-02 can mean only the former.
Dates are sometimes spelled out in cases such as the following:
Dates are spelled out in legal texts and in formal invitations and announcements:
Year designations take the following forms:
Exact age is usually indicated in numerals, even if less than 10:
It is written out, however, in the case of approximate age and in formal contexts:
Market quotations are invariably given in numerals:
Give votes, scores and odds in numerals:
(a) Write out numbers of dynasties, governing bodies, and sessions of Parliament or Congress as ordinals:
(b) Write out ordinal numbers below 100 designating political and administrative divisions:
(c) Designations of large military units, especially in a foreign or historical context, may be written out in ordinals; otherwise use cardinal numerals:
(d) Write out numbers in historical, biblical or formal references:
Ordinals modifying the names of churches and religious bodies are usually written out:
Use Arabic figures in referring to union locals, fraternal lodges and similar organizations:
Use numerals when numbers are referred to as nouns:
Street and avenue designations up to and including Tenth are usually spelled out, especially when this helps to prevent confusion with the building number. If the street name is written in numerals, modern usage tends to favour cardinal rather than ordinal numbers:
In abbreviated form, apartment or suite numbers are written before the building number and are often followed by an en dash:
Identify floors of a building as follows:
Page numbers are usually written in Arabic numerals, but in prefatory material they may be written as lower-case Roman numerals:
Within the body of the text, volume numbers may be indicated by Arabic or Roman numerals or be spelled out. Numbers of chapters and other major divisions of a book may be spelled out, but are more often written in Roman or Arabic numerals—the tendency being away from Roman numerals in the case of both chapter and volume numbers. Verse numbers and those of minor divisions of a book are written as Arabic numerals:
Paragraphs may be numbered 1, 2, . . . ; clauses within paragraphs, 1), 2), . . . . Groups of paragraphs may be numbered with Roman numerals. In citations from legislation and the like, numbers and letters designating parts of a section should be enclosed in parentheses, with no space between them:
See also 4.30 Parts of a book or document.
Plurals of numerals are usually formed by adding an s:
In cases where this might cause misreading, add an apostrophe and s or italicize the numerals:
Whichever practice is adopted, consistency should be maintained in any one document.
Do not pluralize SI/metric symbols:
(a) For general comparisons note the following:
Note that "a four-to-one margin" is meaningless; "a margin of three" is correct.
(b) Consecutive numbers are joined by or or and, except where intermediate quantities are possible:
In references to successive pages, p. 15, 16 indicates matter that is disconnected in the two pages, whereas pp. 15–16 indicates that the subject is continuous from the first page to the second.
(c) Opinions differ on the proper forms for inclusive numbers written as numerals. To ensure clarity, abbreviate second numbers according to the following principles.
Repeat all digits in numbers below 100:
Repeat all digits where the first number is 100 or a multiple of 100:
Where the first number is in the range 101–109, in multiples of 100, use the changed part only and omit unnecessary zeros:
Where the first number is in the range 110–199, in multiples of 100, use two or more digits, as needed:
With numbers of four digits, use all digits if three of them change:
Note the following special cases:
Roman numerals are becoming increasingly rare, but they still have the following uses:
Do not use ordinal forms (st, nd, th, etc.) with Roman numerals.
Lower-case Roman numerals may be used for page numbers in preliminary matter (preface, foreword, table of contents, etc.), subclauses and subordinate classifications in a series.
Note that a bar over a letter in a Roman numeral multiplies its value by 1000:
Clarity should be the primary consideration when communicating numerical information. Present it in such a way that it will be readily grasped by the reader. When writing for non-Canadians, make sure you are aware of the conventions used in the target country. Europeans, for example, who are steeped in the metric system, do not confine themselves as we usually do to multiples of 1000. They will more naturally write 3 dL (decilitres) than 300 mL or 0.3 L. Material written for the European market should conform to this practice.
Remember, too, that in Europe—and in Quebec—1,500 means "one and a half," and 1.500 means "fifteen hundred." The British "billion" is the equivalent of the American "trillion," while a British "trillion" is a million million million. In certain circumstances it may be advisable to write a thousand million or 109 or giga- instead of billion, and a million million or 1012 or tera- instead of trillion, to avoid the risk of misinterpretation. For similar reasons, the abbreviation ppb (parts per billion) should not be used. Rewrite 100 ppb as 0.1 ppm.
Dollar amounts in different currencies should be distinguished from one another by some easily understood marker. A reference to $20 will be ambiguous to a non-Canadian reader and may be taken to refer to American or some other currency. No single system is universally accepted, but the following is the one used by the Department of Finance and the International Monetary Fund:
If greater clarity is required, the abbreviations CAN and AUS may be used. Note that CAD and AUD are also becoming increasingly current.
Where the reader may be in doubt as to which conventions should be followed for writing numerical expressions, the safest course is to adhere to international conventions (see 5.09 Decimal fractions, notes 1 and 2).
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