Overview

Software size variance ( size deviation ) is the difference between a software product’s actual size and its expected or estimated size. This metric is calculated as a percentage. Software size is measured in:

• Lines of Code (LOC)
• Number of Function Points
• Cyclic complexity.

Lines of code (LOC): This is a simple measure of the number of lines in the source code files.

Function points: Function points measure the functionality a software application provides based on the user’s perspective.

Cyclomatic complexity: This metric measures the complexity of the software’s control flow graph, which can indicate the difficulty of understanding and maintaining the code.

Software Size Variance

Size deviation is calculated as follows:

Size deviation =

Actual Size – Estimated Size

———————————   * 100

Estimated Size

Example

In a development project, the application size was estimated to be 80 KLOC. However, at the end of development, it had 100 KLOC. Calculate the project’s size deviation.

The size deviation for the project =   (100 -80 )*100  /80  = 25%

Size deviation is calculated for

a.development projects

b.conversion projects where the conversion involves rewriting code

Size deviation is calculated at the end of each phase. In spiral/iterative model-based development projects, it is calculated at each delivery. The estimated size is taken from the requirement phase or when the last change in requirement was baselined.