International Standards and Conformity Assessment for all electrical, electronic and related technologies
hand typing

Drafting IEC publications



Formulae, equations and variable symbols

(The full requirements are described in the ISO/IEC Directives Part 2:2011, 6.6.10.)


  • The symbols used in each formula should be defined, either in the text above or immediately below the formula.
  • Symbols for variable quantities are to be written in italics.

    Note: We recommend the use of Times New Roman type so as to avoid confusion between the letters i (uppercase i) and l (lowercase L), for example.
  • Subscripts are written in Arial upright type, unless they represent symbols for variable quantities (in which case, they are written in italics).
  • If it is necessary to number some or all of the formulae in a document in order to facilitate cross-reference, Arabic numbers in parentheses are used, beginning with (1).
  • Symbols, rather than descriptive names, shall be used in formulae.


Related topics: