Data units measure the volume of digital information. The foundation is a bit — a single value of 0 or 1. Eight bits make a byte, and each subsequent unit is 1024 times larger than the previous.
That's why a 'gigabyte' on a hard drive package and in your operating system may differ: drive makers count in decimal thousands (1000), while OSes count in binary powers (1024).
Bit and byte
Basics
1 bit = 0 or 1 · 1 byte = 8 bits
A bit is the minimal unit of information — physically one transistor. A byte is historically 'a character': 8 bits hold 256 values (0–255), enough for the English alphabet + control chars (ASCII).
1024 vs 1000
Binary vs SI
1 KiB = 1 024 B · 1 kB = 1 000 B
Drive makers count in decimal thousands (1000): '1 TB' on the box = 10¹² bytes. Operating systems (Windows, Linux) count in binary powers (1024): '1 TiB' = 2⁴⁰ bytes. The gap grows: a 1 TB HDD shows up as ~931 GiB.
MB vs MiB
IEC 60027-2
kB / MB / GB — SI · KiB / MiB / GiB — binary
The IEC 60027-2 (2000) standard introduced Ki, Mi, Gi prefixes for binary powers. In practice 'MB' and 'GB' are still used for both meanings — context decides: networks and drives use SI, memory uses binary.
A pixel is not a byte
Density
1 RGB px = 3 B · 1 RGBA px = 4 B
A colour pixel takes 3 bytes (RGB) or 4 bytes (RGBA). A 1920×1080 raw image is ~6.2 MB, but JPEG compresses it to 300–800 KB. Video and audio are compressed too — otherwise a 4K movie would take terabytes.
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Frequently asked questions
1024, which is what this converter uses: every step up multiplies by 1024. Drive manufacturers and internet providers count in thousands instead, so their gigabyte is the smaller one. Both scales are legitimate — the difference is the base, two for operating systems and ten for packaging.
The multiplier and the standard behind it. A kilobyte under SI is 1000 bytes; a kibibyte under IEC is 1024. The binary prefixes kibi, mebi and gibi were introduced in 1998 precisely to separate the two, but everyday usage never adopted them — Windows still writes GB when it means gibibytes.
A byte is eight bits, so a megabyte is eight times a megabit. Internet providers quote speed in megabits per second while download managers report megabytes, which is why a 100 Mbps line delivers about 12.5 MB/s. The only written difference is the case: Mb against MB.
Between one and four, depending on the encoding and the character. In UTF-8 a Latin letter takes one byte, Cyrillic two, CJK characters three and emoji four. The older single-byte encodings such as windows-1251 gave every character exactly one byte, but they could only hold one alphabet at a time.
Two reasons at once. The manufacturer counts a gigabyte as a billion bytes while the operating system counts 1024 cubed, a gap of about seven percent — a 1 TB drive reports as 931 GB. On top of that, the file system reserves space for its own structures. Neither is a defect.
No. Everything is computed in your browser with ordinary arithmetic, the values you type are never transmitted and nothing is stored. After the first load the page works offline, so you can open it in advance and size a backup where there is no connection at all. Only the name of the opened tool is sent, for a popularity counter.