Supplies - Sending an army that will not starve ?

[Jazzepi]

You can figure out supply from the size of the units. I believe that a normal unit takes up 1 supply by its lonesome. Units with horses, and thus a bigger size unit, take up proportionally more supplies. The same thing is true for elephants, a size 6 unit notorious for creating supply problems.

That should help you get a good estimate of how many supplies you'll need. Note that any supply producing commanders, such as those with nature magic, will reduce the supply demand listed in a province for a given army, so it can mess up your calculations.

Jazzepi