Halstead Software Complexity

The Halstead Complexity calculator computes several code factors based the total and unique number of operators and operands.

INSTRUCTIONS: Enter the following:

• (N₁) Total number of operators
• (N₂) Total number of operands
• (η₁) Number of unique operators
• (η₂) Number of unique operands

Halstead Complexity (HC): The calculator returns the following:

• Program vocabulary
• Program length
• Calculated estimated program length
• Volume of Code
• Software Difficulty 
• Software Effort 
• Time to Write Code
• Estimated Number of Delivered Bugs

The Math / Science

Halstead Complexity calculations were intended to provide software metrics established as an empirical science of software development.  For a software development effort, one can use the following metrics to characterize the level of complexity of developing the software:

• η₁ = the number of distinct operators
• η₂ = the number of distinct operands
• N₁ = the total number of operators
• N₂ = the total number of operands

From these numbers, several measures can be calculated:

• Program vocabulary: η = η₁ + η₂
• Program length: N = N₁ + N₂
• Calculated estimated program length: L = η₁ * log₂(η₁) + η₂* log₂ (η₂)
• Volume of Code: V=N * log₂(η) 
• Software Difficulty: D = (η₁/2) * (N₂ / η₂) 
• Software Effort: E = D*V
• Time to Write Code: T = (E/18) seconds
• Estimated Number of Delivered Bugs: B = V/3000

Note: The difficulty measure is related to the difficulty of the program to write or understand, e.g. when doing code review.