"G Henslee" wrote in message
...

In this case hanging the drywall vertical would result in fewer joints.
If the ceiling was 8'-2" or less, horizontal would be the way.


That's not true of course because they offer 4.5' wide drywall
specifically for 9' ceilings. But even so, it wouldn't necessarily be
correct.
I was not aware of the 4.5 material. But even so, my calculations
wouldn't necessarily be incorrect.

Well no, not necessarily. But neither would they necessarily be correct.
The correct way to do it is the way that results in the fewest butt joints,
and there is no magic guideline that will tell you that without actually
laying it out on paper and calculating it both ways.