The exact definitions
One gigabyte (GB) is exactly 1,000,000,000 bytes, or 10⁹ bytes. One gibibyte (GiB) is exactly 1,073,741,824 bytes, or 2³⁰ bytes. GiB belongs to the IEC system of binary prefixes.
The distinction also applies at other scales: kB and MB are decimal, while KiB and MiB are binary. Capitalization matters, and the lowercase b represents bits rather than bytes.
Why advertised and displayed capacity can differ
Storage manufacturers normally label capacity using decimal units. Some operating systems or applications calculate with binary quantities but may display a decimal-looking label. Formatting, recovery partitions, and filesystem metadata can reduce available space further.
A drive containing 500 GB has 500,000,000,000 bytes. Dividing by 1,073,741,824 gives about 465.66 GiB. No bytes disappeared during that unit conversion; the numerical value changed because the measuring unit is larger.
Bits, bytes, and network speeds
One byte contains eight bits. Storage capacity is commonly expressed in bytes, while network speed is commonly expressed in bits per second. A 1 Gb/s connection has a theoretical maximum of 125 MB/s before protocol and real-world overhead—not 1 GB/s.
- B = byte; b = bit
- GB = 10⁹ bytes
- GiB = 2³⁰ bytes
- Gb/s = 10⁹ bits per second
Which label should you use?
Use GB when the specification is decimal and GiB when the quantity is explicitly binary. When comparing products or troubleshooting capacity, compare the underlying byte count or convert both values into the same unit.
Sources and standards
Definitions were checked against the following primary references: