Hello,
in that case you do not know the capacity that internal components and firmware takes from the drive in order to perform with the host device. so even thought you calculated everything you should take into consideration that the manufacturer stores some firmware information and other stuff inside the drive in order to work.
so i think it would be nice if you would check with sandisk direct to see why you see this different capacities on the drive.
here is the support link:
http://kb.sandisk.com/app/ask/session/L3RpbWUvMTQ1OTc0ODg4NS9zaWQvTHhsNjE5Tm0%3D
