<p>We all know to keep it simple, right?</p>

<p>I've seen complexity being measured as the number of interactions between systems, and I guess that's a very good place to start. Aside from gut feel though, what other (preferably more objective) methods can be used to determine the level of complexity of a particular design or piece of software?</p>

<p>What are YOUR favorite rules or heuristics?</p>

If your app is built, you can measure it in terms of time (how long a particular task would take to execute) or computations (how much code is executed each time the task is run).
If you just have designs, then you can look at how many components of your design are needed to run a given task, or to run an average task. For example, if you use MVC as your design pattern, then you have at least 3 components touched for the majority of tasks, but depending on your implementation of the design, you may end up with dozens of components (a cache in addition to the 3 layers, for example).