This must be one of the most common complaints I see on online shop feedbacks. Manufacturers of storage media state capacity in decimal numbers whereas computers show them in binary.
A 3TB HDD has 3,000,000,000,000 bytes.
To state that in Kilobytes, divide it by 1024 and you get 2,929,687,500 KB
Dividing by 1024 gives you about 2,861,023 MB
Take it one more step and you get 2794 GB
That's 2.738 TB - an
apparent loss of more than a quarter of a TB.
To make matters worse, memory cards and USB flash drives (thumb drives) use up still more space for internal management. That extra used space differs with the model and manufacturer. So, while a 500GB HDD has about 465GB of usable space, a 500GB thumb drive will provide only about 450GB.
This often evokes cries of Counterfeit! Used product! and scathing condemnation of the seller.