Convert data and storage units
Choose the exact unit you mean. Decimal SI units and IEC binary units are represented separately so that GB is not silently treated as GiB.
The important correction: GB and GiB are not the same unit
The earlier version of this tool offered a “1000 or 1024” switch while keeping labels such as KB, MB and GB. That reflects historical software practice, but it mixes two naming systems. In standardized notation, SI prefixes are decimal: 1 kB = 1000 B, 1 MB = 1,000,000 B and 1 GB = 1,000,000,000 B. Binary multiples use IEC prefixes: 1 KiB = 1024 B, 1 MiB = 1,048,576 B and 1 GiB = 1,073,741,824 B.
1 byte equals 8 bits
The byte symbol is uppercase B, while bit is normally written bit. This distinction matters: 1 MB is one megabyte, while 1 Mbit is one megabit. Because one byte contains eight bits, 1 MB corresponds to 8 Mbit when both prefixes use the same decimal scale.
Decimal units: kB, MB, GB, TB and PB
SI prefixes are powers of ten. Kilo represents 10³, mega 10⁶, giga 10⁹, tera 10¹² and peta 10¹⁵. Applied to bytes, that produces exact decimal multiples. This convention is commonly encountered in storage-device capacity, network-rate notation and standards-oriented technical documentation.
Binary units: KiB, MiB, GiB, TiB and PiB
IEC binary prefixes represent powers of 2¹⁰. Kibi (Ki) is 2¹⁰, mebi (Mi) is 2²⁰, gibi (Gi) is 2³⁰, tebi (Ti) is 2⁴⁰ and pebi (Pi) is 2⁵⁰. Therefore 1 GiB is exactly 1,073,741,824 bytes. These names remove the ambiguity created when SI symbols were historically reused for binary quantities.
Why this calculator uses kB instead of KB for decimal kilobyte
In SI notation, the symbol for kilo is lowercase k, so the standards-oriented symbol for kilobyte is kB. Uppercase K is not the SI prefix symbol for kilo. Many operating systems, products and interfaces still display KB for historical or practical reasons, so you will encounter both forms in the real world. This calculator uses kB for the decimal unit and KiB for the binary unit to keep their meanings explicit.
Why a “1 TB” drive can appear smaller in some software
A device advertised as 1 TB using decimal notation contains 1,000,000,000,000 bytes. The same byte count is about 931.323 GiB. If software divides the byte count by powers of 1024 but labels the result as GB instead of GiB, users see a smaller-looking number even though the underlying byte capacity has not disappeared. Formatting, filesystem metadata, partitions and reserved space can introduce additional differences.
MB is not the same as Mbit
Network link rates are commonly expressed in bits per second, such as Mbit/s or Gbit/s, while file sizes are commonly expressed in bytes. An ideal 100 Mbit/s data rate corresponds mathematically to 12.5 MB/s before protocol overhead, encoding, retransmissions and other real-world effects are considered. Do not compare a file size in MB directly with a link rate in Mbit/s without accounting for the factor of eight and time.
Exact unit definitions versus floating-point display
The conversion factors used here are exact definitions for the listed units. The calculator performs arithmetic with PHP floating-point numbers, so extremely large values or results with many fractional digits can be rounded for display. For ordinary storage, memory and networking calculations this is generally sufficient, but applications requiring arbitrary-precision integer accounting should use an appropriate big-integer or decimal library.