The problem of software project cost estimation is still one of the key software engineering challenges. Functional size measurement techniques are widely used as a starting point for other software project cost and effort measurements.

The literature is peppered with techniques for estimating the functional size of a software system. In this context, this paper makes several contributions. First, it offers a fairly comprehensive survey of functional size estimation techniques. This could serve novice researchers and practitioners who intend to use these measurement techniques as a good starting point for accessing more detailed information on the techniques. Additionally, Gencel and Demirors apply several techniques to a number of real cases and identify some lessons learned. These lessons can be divided into two groups targeting different audiences: on the one hand are the recommendations on the use of functional size measurement techniques that can improve the application of the techniques by practitioners; on the other hand, the authors have also discovered needs for improvement of the above techniques. Researchers will undoubtedly find these useful for their research.