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Data sizes trip people up because two conventions are in use at once. Drive makers use decimal units, where 1 KB is 1,000 bytes, while operating systems traditionally use binary ones, where 1 KiB is 1,024 bytes. A drive sold as 1 TB therefore shows up as about 931 GB in Windows, and the missing 7% is this difference rather than any marketing trick. The converters here use the decimal definitions, matching how storage is sold.
The other thing to keep straight is bit against byte. A lowercase b is a bit, an uppercase B is a byte, and there are 8 bits in a byte. File sizes are quoted in bytes and network speeds in bits, which is why the same connection is advertised as a 100 Mbps line and reported as a 12.5 MB/s download.
| b | B | KB | MB | GB | TB | PB | |
|---|---|---|---|---|---|---|---|
| 1 b | 1 | 0.125 | 0.000125 | 1.2500e-07 | 1.2500e-10 | 1.2500e-13 | 1.2500e-16 |
| 1 B | 8 | 1 | 0.001 | 1.0000e-06 | 1.0000e-09 | 1.0000e-12 | 1.0000e-15 |
| 1 KB | 8000 | 1000 | 1 | 0.001 | 1.0000e-06 | 1.0000e-09 | 1.0000e-12 |
| 1 MB | 8.0000e+06 | 1.0000e+06 | 1000 | 1 | 0.001 | 1.0000e-06 | 1.0000e-09 |
| 1 GB | 8.0000e+09 | 1.0000e+09 | 1.0000e+06 | 1000 | 1 | 0.001 | 1.0000e-06 |
| 1 TB | 8.0000e+12 | 1.0000e+12 | 1.0000e+09 | 1.0000e+06 | 1000 | 1 | 0.001 |
| 1 PB | 8.0000e+15 | 1.0000e+15 | 1.0000e+12 | 1.0000e+09 | 1.0000e+06 | 1000 | 1 |
Why does my 1 TB drive show as 931 GB? Because the manufacturer counts decimal terabytes, 1,000,000,000,000 bytes, and the operating system counts binary gibibytes of 1,073,741,824 bytes. Dividing one by the other gives 931.3, so nothing is missing - only the units differ.
How many bits are in a byte? 8, exactly. That is why a 100 Mbps connection downloads at 12.5 MB/s - divide the bits by 8. Confusing the two is the most common error in this category.
Is KB the same as KiB? No. A kilobyte is 1,000 bytes in decimal notation, while a kibibyte is 1,024 bytes. The distinction was formalized in 1998 to end exactly this confusion, though operating systems still often use the older labels.
How many megabytes are in a gigabyte? 1,000 in decimal units, or 1,024 in binary ones. This site uses the decimal value, which is what storage manufacturers and most specification sheets quote.