Consider this quote from a hard drive manufacturer:
It is important to realize that the reported capacity of a large drive may often appear as less than expected. Please remember that, depending on the particular utility used, the capacity of the hard drive can be reported in either decimal gigabytes (where 1 GB = 1,000,000,000 bytes) or in binary gigabytes (where 1 GB = 1,073,741,824 bytes). Highlighting your C: drive in Windows Explorer reports the drive capacity in binary gigabytes. For example, a WD2000BB hard drive’s capacity will be reported as approximately 186 binary gigabytes. For more details about this issue, please see Answer ID 615.
This is a marketing term, NOT a computer term … A gig will always be 1024*1024*1024 … Any “utility” that doesn’t report this based on binary, octal or hexadecimal figures is simply … rubbish …