Horse - -
Maybe Andrew's answer is what you are asking, and I could be wrong so apologies to all if I am, but based on what you wrote:
"if I needed to adjust the zoom from that point, that is after the zoom is determined by your formula..." then maybe you are asking about arriving at a zoom (for what reason I have no idea) based on whatever the zoom would be after the macro runs and determines what the original zoom is, which you wouldn't know as a reference point until you ran the macro.
Example, say you have several rows and columns populated that are wider and longer than 100% zoom if they are to be fit onto a 1x1 printed page. If you want to arrive at a zoom that is, say, 5% less than whatever that "base zoom" would be, then in the macro I posted, replace the line
MsgBox ActiveSheet.PageSetup.Zoom
with the lines:
Dim z As Integer
z = ActiveSheet.PageSetup.Zoom * 0.95
MsgBox z
or you can keep that first message box line in there just to see what the first "base zoom" is when you run the macro, and then the second message box will have that percentage reduced by 5% to give you the final answer to the question you might be asking.
I'd recommend sticking with percentages as multiplicands, not actual numbers as subtractors, because that "base zoom" might be smaller than what you want to subtract from it, and with numbers you'd run the risk of ending up with a negative zoom result, which is just too wierd for me to think about.