Backfiring Function Points from Source Lines of Code

What is this formula?

Backfiring Function Points estimate software size in Function Points (FP) from an existing count of Source Lines of Code (SLOC).

The method is commonly used when source code already exists but a Function Point estimate is required for productivity analysis, cost estimation, benchmarking, or project comparison.

The conversion uses a language-dependent backfiring factor that represents the average number of source lines required to implement one function point.

When to use it

Use this formula when:

- estimating function points from legacy software,

- benchmarking software productivity,

- comparing projects developed in different languages,

- estimating maintenance effort,

- converting historical software metrics.

Example

Suppose an application contains:

SLOC = 50,000 lines

A commonly used backfiring factor is:

BF = 50 lines/FP

Formula:

FP = SLOC / BF

Substitution:

FP = 50,000 / 50

FP = 1,000

Result:

Function Points = 1,000

Applications

- Software estimation

- Legacy system analysis

- Productivity measurement

- Software benchmarking

- Cost estimation

- Portfolio management

Note

Backfiring is an empirical estimation technique. The value of BF varies significantly depending on the programming language, development framework, coding standards, and project characteristics. Typical values may range from fewer than 10 lines per function point for highly productive environments to more than 100 lines per function point for low-level languages. Results should therefore be interpreted as estimates rather than exact measurements.