An estimate is an input output mechanism that represents a method in which a project leader or project team member makes a judgment based on either previous experience or based on a compilation of information that has been gathered via various methods of information gathering is made as to the expected cost of a project in terms of either financial resources needed and/or in terms of man hours that may be needed in completion of this project. This judgment is typically determined through a careful quantitative assessment, and is traditionally applied to a modifier of sorts. Some examples of modifiers in this instance are preliminary, conceptual, feasibility, definitive, and/or order-of-magnitude. It is very important when providing and detailing an estimate via either a written or oral form to provide an indication of accuracy, such as a margin of error in terms of plus or minus percent that an estimate may be off.
This term is defined in the 3rd and the 4th edition of the PMBOK.