File Size Converter

Digital file sizes are counted in bytes, and every larger unit here is a power of 1024 rather than 1000: 1 KB is 2 to the 10th power or 1,024 bytes, 1 MB is 1,048,576 bytes, 1 GB is 1,073,741,824 bytes and 1 TB is 1,099,511,627,776 bytes. The reason is architectural. Memory is addressed with binary address lines, so capacities naturally fall on powers of two, and early programmers borrowed the metric prefix kilo for 1024 because it was within 2.4 percent of 1000. That approximation error compounds with each step, reaching 2.4 percent at KB, 4.9 percent at MB, 7.4 percent at GB and 10.0 percent at TB. The practical consequence is the mismatch users notice on new hardware. Drive manufacturers label capacity in decimal units where 1 TB is exactly 1,000,000,000,000 bytes, while Windows reports the same drive using binary division but still prints the label GB, so a 1 TB disk appears as roughly 931 GB and a 500 GB disk as about 465 GB. No space is missing; only the divisor differs. The unambiguous binary names are kibibyte, mebibyte, gibibyte and tebibyte, abbreviated KiB, MiB, GiB and TiB. Useful reference points for estimating storage: a smartphone JPEG runs 2 to 8 MB, a minute of 1080p video roughly 130 to 500 MB depending on codec and bitrate, a typical office document 50 KB to 5 MB, and a 4K feature film 50 to 100 GB. Note also that network transfer rates are quoted in bits per second, which is 8 times smaller than the byte unit used here.

The byte itself was named by Werner Buchholz at IBM in July 1956 during design work on the Stretch supercomputer, deliberately misspelled to avoid confusion with bit. Its width was not fixed at first; machines of the era used 6-bit and other groupings, and the 8-bit byte became the durable standard with the IBM System/360 announced in 1964, which also made the 8-bit character and byte-addressable memory conventional across the industry. The binary use of metric prefixes spread informally through the 1960s and 1970s because memory chips came in powers of two, and it collided with the decimal convention as soon as disk manufacturers began advertising capacity in round decimal figures. The International Electrotechnical Commission resolved the ambiguity by defining the binary prefixes kibi, mebi, gibi and tebi in a 1999 amendment to IEC 60027-2, a scheme later carried into IEC 80000-13 in 2008 and endorsed by NIST. Adoption has been uneven. Linux tooling and many storage vendors now use KiB and MiB explicitly, and Apple switched macOS to decimal reporting with Mac OS X 10.6 Snow Leopard in 2009, while Windows continues to divide by 1024 and display the label GB. Class-action suits in the United States during the 2000s over capacity labelling led drive makers to add the standard footnote that one gigabyte means one billion bytes.