1. Choose a method based on the objective and available information

According to the AFITEP/AFNOR project management dictionary, "Estimation consists, on the basis of insufficient and often more or less false data, in giving the most probable value and duration of a task (service or supply) performed by third parties over whom we have no possibility of action, at a later (as yet) undetermined time. These values are necessarily accompanied by their degree of confidence".

The aim is to provide an assessment of a project in advance, using data and/or information to be researched.

There are various methods for doing this, each requiring more or less information, data and investment time to obtain a more or less precise estimate, depending on the need.