Simple sum to calculate formatted space?

[OCdude]

I remember there was a simple quick-n-dirty sum for roughly calculating a drives formatted space... i tried to figure it out the other day... i vaguely remember it was something like: capacity x 0.914 or something....

Anyone?

 

[vertica]

your near enough there, (assuming your starting in gigabytes)
capacity(GB)x0.931322574615478515625...
so 0.931 ish

e.g "1TB" unformatted = 1000*0.931 = 931GB formatted

 

[Steve09]

Take away 7% of total space.