[1] Software size is principally measured in function points.
Whilst measuring SLOC is interesting, it is more an indication of effort than functionality.
Two developers could approach a functional challenge using different techniques, and one might need only write a few lines of code, and the other might need to write many times more lines to achieve the same functionality.
One method of software measurement is metrics that are analyzed against the code itself.
[2] There are also more detailed metrics that help measure things like software complexity, Halstead, cohesion, and coupling.