Here's a precise calculation.
Height from plate up to where it starts getting glitchy: 999999 TU
Height from plate down to where it starts getting glitchy: 999999 TU
Total height: 999999 * 2 = 1999998
Total width: --- || ---
Total length: --- || ---
Total area (3D): 19999983 = 7999976000023999992
In studs (3D): 7999976000023999992 * 2 = 15999952000047999984
((999999 * 2) ^ 3) * 2 = 15999952000047999984
Way off buddy.
Though mine was off too, apparantly, so here's a correct version.
The givens:
width = 14,336
length = 14,336
height = 4,999,995 (999999 TU * 5 plates for 1 TU)
The formula:
volume = width * length * height
so the volume is 14,336*14,336*4,999,995.
And that comes out to be a grand total of:
1,027,603,452,395,520 1x1f plates that can be fit into the non-glitchy area of slate.