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Byte Size Converter
Convert a size between decimal and binary units, and see the exact byte count the label really means.
Decimal and binary prefixes are different numbers
A kilobyte (kB) is 1000 bytes; a kibibyte (KiB) is 1024 bytes. The gap compounds: 1 GB = 1,000,000,000 bytes while 1 GiB = 1,073,741,824 bytes, about 7.4% larger. That is why a drive sold as 1 TB reports roughly 931 GiB in an operating system that displays binary units.
SI prefixes (kB, MB, GB) are powers of 1000 and are correct for storage media, networking and Content-Length. IEC prefixes (KiB, MiB, GiB) are powers of 1024 and are common in RAM, file managers and older documentation.
Sizes on the wire and in HTTP
Content-Length is always an exact byte count, never a human label. If a response header says Content-Length: 1048576, that is 1 MiB or about 1.05 MB — not exactly 1 MB. Comparing that number to a stated file size is the fastest way to confirm truncation or an extra transfer encoding.
Frequently asked questions
Why does my 1 TB drive show 931 GB?
The manufacturer uses decimal terabytes (10^12 bytes), while many operating systems divide by 1024 and still print GB. The byte count is unchanged; only the unit convention differs.
Is a megabyte 1000 or 1024 kilobytes?
In SI it is 1000 kB. In binary notation it is 1024 KiB. Mixing the two conventions is the source of most size discrepancies.
What does Content-Length count?
The bytes of the message body after transfer encoding, not characters and not the compressed size if compression happens at another layer.