A Functional Size Unit (FSU) is to software acquisition and development what a square foot is to the building construction industry. An FSU is a standard unit of software size for measuring the functionality of software. It is analogous to a “gallon” of gasoline, a “cord” of wood, or a “meter” of length . “Cord of wood” provides the best analogy because we can only measure by taking a bunch of irregular pieces of wood and filling a space that corresponds to our definition of ‘cord’. In functional sizing, we take different software functional entities (logical data groups and varying types of transactions) and assign weights to them in order to translate the functionality they represent into a quantity of FSUs. The fact that we follow a standard set of rules in the process makes the results consistent across projects and domains.