Include all staff at all levels who are employed by the organisation, whether they are full time, part time, temporary, casual or permanent, but not self-employed contractors.

Express the female median full time equivalent (FTE) annual salary as a percentage of male median FTE salary.   This will give you the gender pay ratio.   Subtract this number from 100 to provide the gender pay gap.   For example, if the median female FTE salary is 84% of the median male salary, the overall gender pay gap is 16%.