The size of the project is measured by 3 factors:
- The number of people working on the project
- The length of the project
- The budget allocated for the project
Most companies solely use the budget as a measure of the size of the project, because the other two factors are nearly always proportional to the budget.
Now perceptions on the size of a project differ based on the size of the company. For example, small companies think that a project with a budget of million dollars to be a huge project, while large companies consider such a project to be a very small project.
So, the size of the project is subjective, but it is always related to the project budget.