This paper introduces the role and importance of the measurement of software sizes when measuring the performance of software activities and in estimating effort, etc, for new software projects. We then describe three standard software sizing methods (the Albrecht/IFPUG, MkII FPA and COSMIC methods) that have claimed to be functional size measurement methods and examine the true nature of their size scales. We find that sizes produced by the Albrecht/IFPUG and MkII FPA methods are actually on a scale of ‘standard (development) effort’. Only the COSMIC method gives a true measure of functional size and is thus best-suited for performance comparisons across projects using different technologies. We conclude that in principle, different types of scales, one measuring functional size and the other standard effort, may be desirable for the different purposes of performance measurement and for estimating, respectively. It then follows that for estimating purposes it might be attractive to define a COSMIC-enabled estimating process in which weights are assigned to the components of a COSMIC functional size dependent on the technology to be used by the project being estimated and maybe on other factors. The resulting COSMIC ‘standard effort’ scale for the given technology, etc., might be expected to yield more accurate project effort estimates than using the standard COSMIC functional size scale. Initial promising results for such an approach are also presented.