The difference is due to way that most storage manufacturers and PC manufacturers define a scale. There are two systems decimal and binary.
Storage devices use a decimal system and PCs use the binary system -this leads to some discrepancy between actual capacity and reported capacity by a PC. The difference can be between about 2% – 9% depending on the capacity of the drive.
Some additional capacity is taken up by features required by the operating system e.g. FAT tables and the flash drive controller e.g. spare blocks for wear levelling.
| Decimal (Dec) bytes | Binary (Bin) bytes | Ratio (Dec/Bin) | % Diff | |||
| Kilobyte | 103 | 1,000 | 210 | 1,024 | 0.9765625 | 2% |
| Megabyte | 106 | 1,000,000 | 220 | 1,048,576 | 0.953674316 | 5% |
| Gigabyte | 109 | 1,000,000,000 | 230 | 1,073,741,824 | 0.931322575 | 7% |
| Terabyte | 1012 | 1,000,000,000,000 | 240 | 1,099,511,627,776 | 0.909494702 | 9% |
