11. Printing of Numbers

Numbers shall be printed in roman (upright) and lightface fonts [ref. 46, ISO 31]. Hence, numerical values of physical quantities (and the symbols for their units) shall be printed in roman, lightface fonts, irrespective of the type used in the rest of the text.

The decimal sign for IUPAC publications in English shall be a point on the line. However, in languages other than English, the comma on the line is often used as the decimal sign, as, for example, in French, German, and Russian.

If the magnitude of the number is less than one, the decimal sign shall be preceded by a zero. For numbers with many digits, the digits may be separated in groups of three, counting from the decimal sign toward the left and the right. The groups should be separated by a thin space (half space), and never by a comma or a point, or by any other means. (This space is best produced as a non-breaking space of constant width, which also prevents splitting of numbers on line breaks. In MS Word for Windows, type ctrl-shift-space; in Mac OS, use command-space.)

When a number with only four digits before or after the decimal sign is given in running text the small space may be left out in order not to isolate a single digit. However, both recommendations about grouping digits into groups of three and not isolating a single digit are to some extent at the discretion of the author. There may be occasions when it is desirable to leave no spaces at all, for example, in numbers to be printed or read by a computer. There shall never be a space in a year written with four digits, for example, 1935 (not 1 935). Similarly, there may be occasions when it is desirable to isolate a single digit, for example, in formatting a column (in a table) of numbers which have varying number of digits before or after the decimal sign.

When uncertainties in the final one or two digits of a numerical value are given as one or two digits in parentheses, there can be either no space or a thin space (half space) between the final digit of the numerical value and the left parenthesis. See also ref. 47.

Examples:

Numbers in a running text: 3.1416 or 3.141 6
Numbers in a column:
  1 000.234 5
21 110.216 48
     500.123 3