Functional size is a measure of the amount of functionality provided by the software, derived by assigning numerical values to the user practices and procedures that the software must perform to fulfill the users’ needs, independent of any technical or quality considerations. The functional size is therefore a measure of what the software must do, not how it should work. This general process is described in the ISO/IEC 14143 standard. The COSMIC method measures the occurrences of Entries, Exits, Reads, and Writes
