Putnam’s model:

The Putnam model is an empirical software effort estimation model. Putnam used his observations about productivity levels to derive the software equation:

(B^1/3.Size)/Productivity=Effort^1/3. Time^4/3

where:

• Size is the product size (whatever size estimate is used by your organization is appropriate). Putnam uses ESLOC (Effective Source Lines of Code) throughout his books.

• B is a scaling factor and is a function of the project size.

• Productivity is the Process Productivity, the ability of a particular software organization to produce software of a given size at a particular defect rate.

• Effort is the total effort applied to the project in person-years.

• Time is the total schedule of the project in years.

In practical use, when making an estimate for a software task the software equation is solved for effort:

Effort=[Size/(Productivity.Time^4/3)]³.B