Data Size Converter: MB, GB, TB
Convert between bytes, KB, MB, GB and TB, in decimal and binary units.
Good to know. Your new 1 TB drive shows 931 GB on a computer. Nobody took anything: the two sides count differently.
How it works
In plain words
Convert the size into bytes, then into the target unit. Decimal units step up by 1,000 (a kilobyte is 1,000 bytes); binary units step up by 1,024 (a kibibyte is 1,024 bytes). A byte is 8 bits.
The formula
1 KB = 1,000 B · 1 MB = 1,000 KB · 1 GB = 1,000 MB 1 KiB = 1,024 B · 1 MiB = 1,024 KiB · 1 GiB = 1,024 MiB 1 byte = 8 bits
Worked example
A 1 TB drive holds 1,000,000,000,000 bytes. Divided by 1,024³ = 1,073,741,824, that is 931.322575 GiB, which Windows shows as “931 GB”.
Sources
- NIST, Prefixes for binary multiples KiB, MiB, GiB and TiB, as defined in IEC 80000-13.
Sources checked September 30, 2026. 4 automated tests check its answers on every change.
About the data size converter: MB, GB, TB
Storage and file sizes are counted in bytes, and there are two ways to scale them up. Drive makers, phone makers and network speeds use decimal prefixes, like the rest of the metric system: a kilobyte is 1,000 bytes, a megabyte 1,000,000 and a gigabyte a billion. Computers work in powers of two, so memory and many operating systems count a “kilobyte” as 1,024 bytes.
To tell them apart, the IEC introduced binary prefixes: kibibyte (KiB, 1,024 bytes), mebibyte (MiB), gibibyte (GiB) and tebibyte (TiB). The gap grows with each step: 2.4% for kilo, 7.4% for giga and almost 10% for tera. That is why a 1 TB drive shows up as about 931 GB in Windows, which uses binary units with decimal names. macOS, iOS and Android count in decimal, and show the full 1 TB.
Internet speeds are in bits, not bytes: a 100 Mb/s connection moves at most 12.5 megabytes a second, before overheads. Divide by 8 to go from bits to bytes.
The table shows your value in every unit at once, decimal and binary.
Questions people ask
How many MB are in a GB?
1,000 in decimal units, used for storage and data plans. In binary units, a GiB is 1,024 MiB.
Why does my 1 TB drive show only 931 GB?
The drive holds 1,000,000,000,000 bytes. Windows divides by 1,024 three times and calls the result GB, which gives 931.
What is the difference between Mb and MB?
Mb is megabits and MB is megabytes. A byte is 8 bits, so 100 Mb/s is 12.5 MB/s.