This 2.5-inch hard drive has a capacity of 500 gigabytes (GB) of data (i.e., 500 billion bytes).
Multiple-byte units
Value Metric
1000 kB kilobyte
10002 MB megabyte
10003 GB gigabyte
10004 TB terabyte
10005 PB petabyte
10006 EB exabyte
10007 ZB zettabyte
10008 YB yottabyte
10009 RB ronnabyte
100010 QB quettabyte
Value IEC Memory
1024 KiB kibibyte KB kilobyte
10242 MiB mebibyte MB megabyte
10243 GiB gibibyte GB gigabyte
10244 TiB tebibyte TB terabyte
10245 PiB pebibyte
10246 EiB exbibyte
10247 ZiB zebibyte
10248 YiB yobibyte
Orders of magnitude of data

The gigabyte (/ˈɡɪɡəbt, ˈɪɡəbt/)[1] is a multiple of the unit byte for digital information. The prefix giga means 109 in the International System of Units (SI). Therefore, one gigabyte is one billion bytes. The unit symbol for the gigabyte is GB.

This definition is used in all contexts of science (especially data science), engineering, business, and many areas of computing, including storage capacities of hard drives, solid-state drives, and tapes, as well as data transmission speeds. The term is also used in some fields of computer science and information technology to denote 1073741824 (10243 or 230) bytes, however, particularly for sizes of RAM. Thus, some usage of gigabyte has been ambiguous. To resolve this difficulty, IEC 80000-13 clarifies that a gigabyte (GB) is 109 bytes and specifies the term gibibyte (GiB) to denote 230 bytes. These differences are still readily seen, for example, when a 400 GB drive's capacity is displayed by Microsoft Windows as 372 GB instead of 372 GiB. Analogously, a memory module that is labeled as having the size "1GB" has one gibibyte (1GiB) of storage capacity.

In response to litigation over whether the makers of electronic storage devices must conform to Microsoft Windows' use of a binary definition of "GB" instead of the metric/decimal definition, the United States District Court for the Northern District of California rejected that argument, ruling that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce.'"[2][3]


The term gigabyte has a standard definition of 10003 bytes, as well as a discouraged[2] meaning of 10243 bytes. The latter binary usage originated as compromise technical jargon for byte multiples that needed to be expressed in a power of 2, but lacked a convenient name. As 1024 (210) is approximately 1000 (103), roughly corresponding to SI multiples, it was used for binary multiples as well.

In 1998 the International Electrotechnical Commission (IEC) published standards for binary prefixes, requiring that the gigabyte strictly denote 10003 bytes and gibibyte denote 10243 bytes. By the end of 2007, the IEC Standard had been adopted by the IEEE, EU, and NIST, and in 2009 it was incorporated in the International System of Quantities. Nevertheless, the term gigabyte continues to be widely used with the following two different meanings:

Base 10 (decimal)

Based on powers of 10, this definition uses the prefix giga- as defined in the International System of Units (SI). This is the recommended definition by the International Electrotechnical Commission (IEC).[4] This definition is used in networking contexts and most storage media, particularly hard drives, flash-based storage,[5][6] and DVDs, and is also consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance. The file manager of Mac OS X version 10.6 and later versions are a notable example of this usage in software, which report files sizes in decimal units.[7]

Base 2 (binary)

The binary definition uses powers of the base 2, as does the architectural principle of binary computers. This usage is widely promulgated by some operating systems, such as Microsoft Windows in reference to computer memory (e.g., RAM). This definition is synonymous with the unambiguous unit gibibyte.

Consumer confusion

Since the first disk drive, the IBM 350, disk drive manufacturers expressed hard drive capacities using decimal prefixes. With the advent of gigabyte-range drive capacities, manufacturers labelled many consumer hard drive, solid-state drive and USB flash drive capacities in certain size classes expressed in decimal gigabytes, such as "500 GB". The exact capacity of a given drive model is usually slightly larger than the class designation. Practically all manufacturers of hard disk drives and flash-memory disk devices[5][6] continue to define one gigabyte as 1000000000bytes, which is displayed on the packaging. Some operating systems such as Mac OS X[8] and Ubuntu,[9] and Debian[10] express hard drive capacity or file size using decimal multipliers, while others such as Microsoft Windows report size using binary multipliers. This discrepancy causes confusion, as a disk with an advertised capacity of, for example, 400 GB (meaning 400000000000bytes, equal to 372 GiB) might be reported by the operating system as "372 GB".

For RAM, the JEDEC memory standards use IEEE 100 nomenclature which quote the gigabyte as 1073741824bytes (230 bytes).[11]

The difference between units based on decimal and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the decimal kilobyte value is nearly 98% of the kibibyte, a megabyte is under 96% of a mebibyte, and a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB (279 GiB) hard disk might be indicated variously as "300 GB", "279 GB" or "279 GiB", depending on the operating system. As storage sizes increase and larger units are used, these differences become more pronounced.

US lawsuits

A lawsuit decided in 2019 that arose from alleged breach of contract and other claims over the binary and decimal definitions used for "gigabyte" have ended in favor of the manufacturers, with courts holding that the legal definition of gigabyte or GB is 1 GB = 1,000,000,000 (109) bytes (the decimal definition). Specifically, the courts held that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce' .... The California Legislature has likewise adopted the decimal system for all 'transactions in this state'."[2]

Earlier lawsuits had ended in settlement with no court ruling on the question, such as a lawsuit against drive manufacturer Western Digital.[12][13] Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.[12] Seagate was sued on similar grounds and also settled.[12][14]

Other contexts

Because of their physical design, the capacity of modern computer random-access memory devices, such as DIMM modules, is always a multiple of a power of 1024. It is thus convenient to use prefixes denoting powers of 1024, known as binary prefixes, in describing them. For example, a memory capacity of 1073741824bytes (10243 B) is conveniently expressed as 1 GiB rather than as 1.074 GB. The former specification is, however, often quoted as "1 GB" when applied to random-access memory.[15]

Software allocates memory in varying degrees of granularity as needed to fulfill data structure requirements and binary multiples are usually not required. Other computer capacities and rates, like storage hardware size, data transfer rates, clock speeds, operations per second, etc., do not depend on an inherent base, and are usually presented in decimal units. For example, the manufacturer of a "300 GB" hard drive is claiming a capacity of 300000000000bytes, not 300 × 10243 (which would be 322122547200) bytes.

Examples of gigabyte-sized storage

Unicode character

The "gigabyte" symbol is encoded by Unicode at code point U+3387 SQUARE GB.[16]

See also


  1. ^ The prefix giga- may be pronounced two ways.
    • "gigabyte". Unabridged (Online). n.d.
    • "gigabyte". Dictionary.
  2. ^ a b c "Order Granting Motion to Dismiss" (PDF). United States District Court. Retrieved 24 January 2020.
  3. ^ See also Dinan v. SanDisk LLC, No. 20-15287 (9th Cir. Feb. 11, 2021)
  4. ^ Prefixes for binary multiples
  5. ^ a b SanDisk USB Flash Drive Archived 13 May 2008 at the Wayback Machine "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes."
  6. ^ a b Storage Chart "Megabyte (MB) = 1,000,000 bytes; 1 Gigabyte (GB) = 1,000,000,000 bytes; 1TB = 1,000,000,000,000 bytes"
  7. ^ "How Mac OS X reports drive capacity". Apple Inc. 27 August 2009. Retrieved 16 October 2009.
  8. ^ "How OS X and iOS report storage capacity - Apple Support". Retrieved 29 June 2016.
  9. ^ "UnitsPolicy". Ubuntu Wiki. Ubuntu. Archived from the original on 18 November 2021. Retrieved 9 January 2022.
  10. ^ "ConsistentUnitPrefixes". Debian Wiki. Archived from the original on 3 December 2021. Retrieved 9 January 2022.
  11. ^ JEDEC Solid State Technology Association (December 2002). "Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits" (PDF). Jesd 100B.01.
  12. ^ a b c Mook, Nate (28 June 2006). "Western Digital Settles Capacity Suit". betanews. Retrieved 30 March 2009.
  13. ^ Baskin, Scott D. (1 February 2006). "Defendant Western Digital Corporation's Brief in Support of Plaintiff's Motion for Preliminary Approval". Orin Safier v. Western Digital Corporation. Western Digital Corporation. Retrieved 30 March 2009.
  14. ^ Judge, Peter (26 October 2007). "Seagate pays out over gigabyte definition". ZDNet. Retrieved 16 September 2014.
  15. ^ Percival, Colin. "Why is 1 GB equal to 10^9 bytes instead of 2^30?". Retrieved 1 November 2015.
  16. ^ Unicode Consortium (2019). "The Unicode Standard 12.0 – CJK Compatibility ❰ Range: 3300—33FF ❱" (PDF). Archived (PDF) from the original on 3 June 2001. Retrieved 24 May 2019.