5.10 Quantities and measures

(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):

• three miles
• 5.6 km
• 20/20 vision
• a magnification of 50 or a 50 × magnification
• two metres tall
• 1.6 m tall not 1 m 60 cm tall
• six feet tall
• 5 feet 11 inches tall (no comma between elements)
• 8½ by 11 inch paper or 8½ × 11 inch paper
• 50 cm × 75 cm × 2 m (unit repeated to avoid ambiguity)

(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:

• two metres or 2 m

not

• 2 metres or two m

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:

• 5 lb. or about 2.3 kg

(d) Note the following conventions for using the degree symbol:

• 40 proof
• 30 °C–50 °C (symbol repeated) but 30±2 °C
• 10–15 °C
• –10 to –15 °C not –10–15 °C
• 10 °C
• 10.5 °C
• 300 K not 300°K
• 10° (of arc)
• 10.5° or 10.°5 or 10°30’ or 10°30’00’’
• 36°N lat.
• 36th parallel
• mm/degree not mm/° (° not to be used alone in denominator)

See 1.17 Number and percentage symbols for use of the term percent and the percent sign.

5.26 Other considerations

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 $20 will be ambiguous to a non-Canadian reader and may be taken to refer to American or some other currency. The Translation Bureau recommends the symbol Can$ to represent the Canadian dollar:

• Can$20

Note: The abbreviation Can$ is sometimes written entirely in upper case: CAN$20.

Although C$ is another symbol frequently used for the Canadian dollar, the Translation Bureau does not recommend it. Since this symbol is also used for the Nicaraguan córdoba oro and occasionally for the Cayman Islands dollar as well, it might lead to confusion in some contexts.

In international or financial texts, the code CAD is often preferred. This code is the one established by the International Organization for Standardization to represent the Canadian dollar; it is composed of the country symbol CA (Canada) and the currency symbol D (dollar). Since this code already contains the symbol D for "dollar," the dollar sign would be redundant and should be omitted. The code is placed before the dollar figure, with a non-breaking space between:

• CAD 30 million

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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