Over the years there has been a constant battle between storage engineers and hard drive companies on whether or not advertised hard drive sizes are misleading to consumers. The advertised numbers are in fact misleading because they do not state the actual usable size of the hard drive being sold. In order to find the corrected size of a hard drive you must account for the actual allocation size used by the hard drive manufacturer.
When a 300GB hard drive is sold the manufacturer is stating that the hard drive has a capacity which meets the following equation:
300GB = 300,000,000,000 bytes
With a 300GB hard drive the manufacturer would like you to think the above equation is true. It in fact is not. The reason why this value is false is because 1,000 bytes should be represented as 1,024 bytes. So in order to find the true size of a 300GB hard drive you must divide by 1024 three times to calculate its true size in Gigabytes.
300,000,000,000 bytes ÷ 1024 = 292,968,750 Kilobytes
292,968,750 kilobytes ÷ 1024 = 286,102.3 Megabytes
286,102.3 Megbytes ÷ 1024 = 279.3968 Gigabytes
The corrected size of an advertised 300GB drive is actually 279GB and change.
If hard drive manufacturers gave you the advertised capacity of 300GB the drive would have to be 322,122,547,200 Bytes in size. This can be calculated by multiplying 300GB x 1024 three times to find the required bytes.