Army size

In game players army size is listed from largest to smallest, but how is this figure determined?

For example in terms of army size how is a battleship compared to a militia?

Crew size? Balanced units.

To increase your army size quickly can you build a lot of cheap units like militia?

Hence someone that has a lot of expensive units to build may have a small army size wise, but their army would probably be stronger.

Army size doesn't always relate directly to Army strength.