What disk management shows is all you have. GB are a variable when disc size advertised.
Since the early 2000s most of consumer hard drive capacities are grouped in certain size classes measured in gigabytes. The exact capacity of a given drive is usually some number above or below the class designation. Although most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as 1000000000bytes, the computer operating systems used by most users usually calculate size in gibibytes by dividing the total capacity in bytes by 1073741824, but report the result with the symbol GB. This practice can be a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes may be reported by the operating system as only 372 GB. Notable exceptions in such usage are some components of Linux Kerne