Actual Storage on 256gb SanDisk Ultra Dual Drive m3.0


I just bought a SanDisk Ultra Dual Drive m3.0 with 256gb.I knew there is different conversion for the actual capacity show on computer with what advertised by manufacturer.

By calculation,256gb/(1024^3)=238gb.But it only showed the capacity as 234gb on my computer with windows 10.

There might have some capacites used for formatting and other function for the drive,but did the flashdrive need 4gb to do the formatting and other function ???