10gb 10.000.000.000 10gb 9.69 6.69 percemt
20gb 20.000.000.000 20gb 18.6 6.75 percent
30gb 30.000.000.000 30gb 27.94 6.68666666666666666666666666666667 percent to be exact
100gb 100.000.000.000 100gb 93,13 6.87
500gb 500.000.000.000 500gb 465,65 6.87
100gb 1.000.000.000.000 1000gb 931.30 6.87 also
I did the math here are the exact numbers for different gigibytes didn't have the time to do them all but most average out to be 6.87
It's not an arithmetic constant.
What about- say- 400 Yottabytes?
483,570,327,845,852,000,000,000,000 bytes according to a PC
400,000,000,000,000,000,000,000,000 bytes if there was a 400TB HD manufactured.
approx. 20% difference.
the reason for this difference has been explained. there simply is no "average" and like most "rules of thumb" woefully inaccurate.
10GB according to a PC is 10*1024*1024*1024, or 10,737,418,240 bytes.
However hard drives are sold differently- a 10GB drive will likely actually be 10,000,000,000 bytes.
EDIT:
last nitpick:
6.68666666666666666666666666666667 percent to be exact
No, to be exact would require infinite 6's.