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3 Examples of a Fudge Factor

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A fudge factor is a number based on observed results as opposed to solid theory, logic or calculations. They are commonly used as a practical measure to overcome uncertainty or complexity. The following are examples.


Einstein included an invented "cosmological constant" in his general theory of relativity because his results indicated that the universe was expanding or contracting. This didn't seem right to him, so he included the constant to cancel this out. He later referred to this as "the biggest blunder of my life" as it is now accepted that the universe is indeed expanding.
It is a common practice in science to include fudge factors that derive from measured observations that aren't necessarily explainable with theory and calculation.


Fudge factors may be used in engineering calculations to mitigate risks. These are typically given more formal names as "fudge factor" is commonly interpreted to have negative connotations. For example, an engineer may make a tire 4x stronger than required by anticipated road conditions. The choice of the constant 4 may be somewhat arbitrary.

Project Management

A project manager may apply a margin of safety into estimates. This may be done using a fudge factor such as multiplying estimates supplied by subject matter experts by 1.5.
Overview: Fudge Factor
Definition (1)
A number that fits observations but not theory.
Definition (2)
An ad-hoc number that is invented for practical reasons such as mitigating risk.
In science, a fudge factor is typically used openly to represent observations that don't fit a theory.
In engineering, a fudge factor may be given a technical name that makes it sound less ad-hoc.
In project management, a fudge factor may be an unwritten rule within an organization that isn't officially acknowledged.
Related Concepts


This is the complete list of articles we have written about estimates.
Change Analysis
Fudge Factor
Schedule Risk
Scope Risk
Story Points
Work Complexity
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