A software metric is a measure of some property of a piece of software or its specifications.
Since quantitative methods have proved so powerful in the other sciences, computer science practitioners and theoreticians have worked hard to bring similar approaches to software development. Tom DeMarco stated, “You can’t control what you can't measure” in DeMarco, T. (1982) Controlling Software Projects: Management, Measurement & Estimation, Yourdon Press, New York, USA, p3.
Common software metrics include:
Order of growth (See Analysis of algorithms in terms of Asymptotic analysis and Big O notation)
Source lines of code
Cyclomatic complexity
Function point analysis
Bugs per line of code
Code coverage
Number of lines of customer requirements.
Number of classes and interfaces
Robert Cecil Martin’s software package metrics
Cohesion
Coupling
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http://en.wikipedia.org/wiki/Software_metrics