Byte Size Converter (KB / KiB / MB / MiB / ...)

There are two conflicting standards for byte units. SI/decimal: 1 KB = 1000 B, 1 MB = 1 000 000 B. IEC/binary: 1 KiB = 1024 B, 1 MiB = 1 048 576 B. Disk manufacturers use decimal. RAM and most OSes use binary but often label it with the SI prefix (Windows showing 'GB' that's really GiB). This calculator shows both side-by-side so you don't have to guess which one your tool means. Also includes bits for network bandwidth conversions.

The gap widens at every step, which is why the confusion gets worse the larger the number. A kilobyte and a kibibyte differ by 2.4 percent, a megabyte and a mebibyte by 4.9, a gigabyte and a gibibyte by 7.4, and a terabyte and a tebibyte by 10. That last figure is the whole of the missing-disk-space complaint: a drive sold as 1 TB holds a trillion bytes, which Windows reports as 0.91 TB because it means TiB, and nothing has been lost.

RAM is the exception that is genuinely binary. Memory is addressed in powers of two because of how address lines work, so a 16 GB module really is 16 GiB and the label is the one that is wrong rather than the quantity. Storage has no such constraint, which is why manufacturers were free to adopt the decimal reading and did.

Operating systems disagree with each other as well as with the labels. macOS has reported decimal since 10.6, so the same drive reads as 1 TB there and 931 GB in Windows, and Linux tools split by convention: ls -l gives bytes, ls -lh gives binary, and df depends on the flag. A number copied between two systems without noting which convention produced it is off by a percentage that grows with the unit.

Bits are a separate axis and the most common error of all. Network rates are quoted in bits per second while file sizes are in bytes, so dividing a download size by a connection speed without the factor of eight overstates the time by that much.