I'm seriously fed up with companies calculating in decimal.
buy 1tb = 931gb...
So yea, my question is: are there any companies which I can give my money to so I can get a nice 240gb ssd?
No. 1TB = 1000GB. And decimal is actually correct, since "tera", "giga", "mega" etc. are decimal unit prefixes.
The Problem is, that windows reports it in gibibyte instead of gigabyte (while still wrongly calling it gigabyte). So 1 TB = 931 GiB (not GB!).
As far as I know, Linux uses the decimal sizes and therefore shows drive sizes correctly, without causing this confusion.
So you've got to blame the OS/Software, not the hardware.