Costing Techniques

COCOMO -- Constructive Cost Model

COCOMO is good for large-scale software projects. For small-scale projects, the LOC cost table and the labor cost/task table techniques are more appropriate.
E = (a + b S^c) m(x1, x2, ..., xn)
where E is effort (person-months), S is estimated system size (LOC), a, b and c are constants, and m is a cost multiplier based on cost factors x1, x2, ..., xn.
A simpler formula does not have the additive cost (fixed cost) a and the cost multiplier m.
E = b S^c
For example, based upon IBM project data, Walston and Felix concludes that
E = 5.25 S^0.91