5.09 Decimal fractions

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:

  • $0.64 not $.64
  • 11 or 11.0 not 11.


  • a .39 calibre revolver
  • .999 fine gold

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.

Note 1

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.

Note 2

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:

whole numbers decimals
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.