How do you define Project Complexity?

Maybe I'm simplifying it too much but I equate the complexity to the number of deliverables in the process. For my area Engineering Procurement & Construction I define the Project by compiling the deliverables which simply defined is each step in the process by each individual accomplishing that process. So you have an action by an individual that produces a tangible product in the process. It could be a drawing by an engineer in the design phase, a submittal by a contractor in the construction phase or the review of such deliverables or the installation of the product. Once you define the participants, the actions and the products you have the deliverables and that total number will give you the complexity. Simple addition to a building 1,500 deliverables - not so complex, Theme Park 280,000 deliverables - very complex

Maede & Steve made some very good and key points. I fully agree with this.

Expert judgement on how to evaluate things like this plays a major role.

I agree with my colleagues here.
I think better understanding of project complexity and creating a strategy to manage complexity, influences how efficiently and economically projects are planned,managed,and executed.

George - in most cases, people have a hard time agreeing on the level of complexity, but the real understanding of it usually comes with experience. Here's a good article I've found (thanks for inspiring me to look:) https://www.projecttimes.com/articles/intr...del-part-i.html

We consider some criterias:
1 - Project size
2 - Project type: Technology or organizational innovation
3 - Location and number of project teams
4 - Project impact
5 - Level of dependency with other projects
6 - Number of organizations involved
We have a weighted average to define the complexity.