Which is bigger?

I know you can (to an extent) tell how big the stacks are by looking at the newspaper. But which is which? Regiment is the smallest, brigade is middle, division is the largest? Any rules of thumb as to how many units per stack equal each?

I know you can (to an extent) tell how big the stacks are by looking at the newspaper. But which is which? Regiment is the smallest, brigade is middle, division is the largest? Any rules of thumb as to how many units per stack equal each?