Context: One of the difficulties faced by software development Project Managers is estimating the cost and schedule for new projects. Previous industry surveys have concluded that software size and cost estimation is a significant technical area of concern. In order to estimate cost and schedule it is important to have a good understanding of the size of the software product to be developed. There are a number of techniques used to derive software size, with function points being amongst the most documented.Objective: In this paper we explore the utility of function point software sizing techniques when applied to two levels of software requirements documentation in a commercial software development organisation. The goal of the research is to appraise the value (cost/benefit) which functional sizing techniques can bring to the project planning and management of software projects within a small-to-medium sized software development enterprise (SME). Method: Functional counts were made at the bid and detailed functional specification stages for each of five commercial projects used in the research. Three variants of the NESMA method were used to determine these function counts. Through a structured interview session, feedback on the sizing results was obtained to evaluate its feasibility and potential future contribution to the company.Results: The results of our research suggest there is value in performing size estimates at two appropriate stages in the software development lifecycle, with simplified methods providing the optimal return on effort expended. Conclusion: The ‘Estimated NESMA’ is the most appropriate tool for use in size estimation for the company studied. The use of software sizing provides a valuable contribution which would augment, but not replace, the company’s existing cost estimation approach.