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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 notm 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


  • 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:

  • 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.