ABC metric

The ABC metric is a size measure proposed by Jerry Fitzpatrick in 1997. It counts three types of syntactic features and reports them as a vector and as a magnitude. The vector <A, B, C> is reported alongside the magnitude |ABC| = sqrt(A² + B² + C²).

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What mehen emits

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How to read it

There is no universal threshold, but Fitzpatrick’s original paper proposed: The Ruby community adopted ABC widely via rubocop-rubycop/rubycritic, which uses <A, B, C> and a magnitude threshold of 17 by default for methods.

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Per-language increments

Each language analyzer maps its statement and expression node kinds onto the three buckets. The canonical mapping:

• Assignments: =, +=, −=, *=, /=, %=, <<=, >>=, &=, |=, ^=, prefix/postfix ++/−−, parameter default values where applicable.
• Branches: function calls, method calls, constructors, super(...) calls, and dynamic dispatch.
• Conditions: if, else if, case/when, ternary, && / ||, equality and ordering operators, exception handlers (catch, rescue, except).

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References

• Fitzpatrick, J. (1997). Applying the ABC Metric to C, C++, and Java. C++ Report, June 1997. Author archive (PDF).
• RuboCop: Metrics/AbcSize cop documentation — production-grade Ruby implementation with documented thresholds.

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See also

• Cyclomatic complexity — counts branches/conditions differently.
• LOC family — orthogonal size measure.