What is the stacking limit (16 units or less)?

Anyone understand the stacking limits in this game? I know you can't have more than 16 units stacked together on the strategic map (and hence on the battlefield). But sometimes I have less than 16 and I get a message "there is no more room for a unit of that size". Does anyone know what the size limit is, beyond the 16 unit thing? I'm particularly interested to know if it is counted in men, men+horses or some weighted combination etc.
Thanks for any advice.

The maximum number of men that can be put in a stack is dependent on the unit size slider. On default the limit is 960, on medium it is approx 1280, & on large it is 1600. I don't know what the small & extra large limits are, probably about 800 & 2000 or so.

Don Coyote

Thanks, Don, that's interesting. So you could only have nine units of 100 spearmen in the default game? That eases some of my concerns about being able to get more spears than other kinds of infantry.