A gigabyte (GB, also written GByte) is a decimal data unit equal to 1,000,000,000 bytes (109 bytes). It is different from a gibibyte (GiB), which equals 1,073,741,824 bytes (230). Use GB for the decimal unit and GiB for the binary unit whenever the exact byte count matters.
Gigabyte definition
In the International System of Units (SI), giga means 109. Therefore:
- 1 GB = 109 bytes = 1,000,000,000 bytes
- GB is the standard compact symbol; GByte is an alternate written form.
The capital B denotes bytes. A lowercase b conventionally denotes bits, so GB and Gb describe different quantities.
GB versus GiB
| Unit | Meaning | Exact number of bytes |
|---|---|---|
| GB (gigabyte) | Decimal, 109 bytes | 1,000,000,000 |
| GiB (gibibyte) | Binary, 230 bytes | 1,073,741,824 |
The binary prefix gibi and symbol Gi were introduced to remove the ambiguity created when “gigabyte” was used for both decimal and binary quantities. The International Electrotechnical Commission approved the binary-prefix series in December 1998, according to the National Institute of Standards and Technology (NIST).
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Why the terminology became confusing
Early computing commonly used “kilo” for 1,024 because 210 is close to 1,000 and computer memory is organized in powers of two. As storage, memory and telecommunications developed different conventions, the same prefix came to represent different quantities. Modern technical writing resolves this by reserving SI prefixes such as giga for powers of ten and using binary prefixes such as gibi for powers of two.
Where gigabytes are used
Storage capacity
Drive and media capacities can be stated in gigabytes to describe a quantity of stored bytes. To interpret a capacity precisely, check whether the specification uses GB or GiB and compare the underlying byte count.
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Memory capacity
RAM and other memory specifications may be discussed using gigabytes or gibibytes. Do not assume that a number labeled “GB” represents 230 bytes; the symbol determines the formal unit, while a particular product or software interface may follow its own documented convention.
Files and data transfers
File sizes are quantities of bytes. A transfer rate adds a time basis, such as megabytes per second (MB/s). Bits and bytes must not be conflated: eight bits make one byte, and a rate in megabits per second (Mb/s) is not the same as a rate in megabytes per second (MB/s).
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How to compare a capacity correctly
- Identify the quantity: determine whether the value is bytes (B) or bits (b).
- Check the prefix: distinguish decimal GB from binary GiB.
- Read any time basis: “per second” indicates a data rate rather than a capacity.
- Compare bytes: convert both values to an explicit byte count before deciding whether they are equal.
- Check the product or software documentation: operating systems, applications and manufacturers may display units differently, and their conventions require product-specific documentation.
Notation rules
- Write GB, not “G B”; prefix symbols attach directly to the unit symbol.
- Use GiB when you mean 230 bytes.
- Use an uppercase B for bytes and a lowercase b for bits.
- Define the convention when a capacity comparison could otherwise be ambiguous.
Key takeaway
A gigabyte is formally one billion bytes. A gibibyte is a separate binary unit containing 1,073,741,824 bytes. Stating GB or GiB—and bytes or bits—prevents the most common capacity and transfer-rate misunderstandings.
Quick Recap
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