Function point

A unit of software size based on what the system does for users, independent of the programming language.

Function points count inputs, outputs, queries, internal files and interfaces, weighted by complexity. Because they do not depend on the language, they let you compare projects and convert lines of code into size using published tables of lines per function point. Historical data then turns size into effort.

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Related terms

Reference class forecasting: Estimating from what similar finished projects actually cost, instead of from your own feature list.
Cone of uncertainty: How wide an honest estimate is at each stage: from 0.25× to 4× at the idea stage, narrowing as decisions are made.
Fixed price: A contract where scope and price are agreed up front and the vendor carries the risk.

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