Kilobyte#Base 2 (1024 bytes)

In the International System of Units (SI) the metric prefix kilo means 1,000 (10³); therefore, one kilobyte is 1000 bytes. The unit symbol is kB.

This is the definition standardised by the International Electrotechnical Commission (IEC).[http://physics.nist.gov/cuu/Units/binary.html Prefixes for Binary Multiples] {{webarchive|url=https://web.archive.org/web/20070808000831/http://physics.nist.gov/cuu/Units/binary.html |date=2007-08-08 }} — The NIST Reference on Constants, Units, and Uncertainty This definition, and the related definitions of the prefixes mega ({{gaps|1,000,000}}), giga ({{gaps|1,000,000,000}}), etc., are most commonly used for data transfer rates in computer networks, internal bus, hard drive and flash media transfer speeds, and for the capacities of most storage media, particularly hard disk drives,1977 Disk/Trend Report Rigid Disk Drives, published June 1977 flash-based storage,[http://apac.sandisk.com/Products/Catalog(1349)-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx SanDisk USB Flash Drive] {{webarchive|url=https://web.archive.org/web/20080513155718/http://apac.sandisk.com/Products/Catalog%281349%29-SanDisk_Extreme_Ducati_Edition_USB_Flash_Drive.aspx |date=2008-05-13 }} "Note: 1 megabyte (MB) = 1 million bytes; 1 gigabyte (GB) = 1 billion bytes." and DVDs. It is also consistent with the other uses of the metric prefixes in computing, such as CPU clock speeds or measures of performance.

The international standard IEC 80000-13 uses the term "byte" to mean eight bits (1 B = 8 bit). Therefore, 1 kB = 8000 bit. One thousand kilobytes (1000 kB) is equal to one megabyte (1 MB), where 1 MB is one million bytes.

The term 'kilobyte' has traditionally been used to refer to 1024 bytes (2¹⁰ B).[http://www.merriam-webster.com/dictionary/kilobyte Kilobyte – Definition and More from the Free Merriam-Webster Dictionary] {{webarchive|url=https://web.archive.org/web/20100409171320/http://www.merriam-webster.com/dictionary/kilobyte |date=2010-04-09 }}. Merriam-webster.com (2010-08-13). Retrieved on 2011-01-07.[http://dictionary.reference.com/browse/kilobyte Kilobyte | Define Kilobyte at Dictionary.com] {{webarchive|url=https://web.archive.org/web/20100901202451/http://dictionary.reference.com/browse/kilobyte |date=2010-09-01 }}. Dictionary.reference.com (1995-09-29). Retrieved on 2011-01-07.[http://www.askoxford.com/concise_oed/kilobyte?view=uk Definition of kilobyte from Oxford Dictionaries Online] {{webarchive|url=https://web.archive.org/web/20060625132017/http://www.askoxford.com/concise_oed/kilobyte?view=uk |date=2006-06-25 }}. Askoxford.com. Retrieved on 2011-01-07. The usage of the metric prefix kilo for binary multiples arose as a convenience, because 1024 is approximately 1000.{{cite web|title=Prefixes for binary multiples|url=http://www.iec.ch/si/binary.htm|website=iec.ch|publisher=International Electrotechnical Commission|access-date=1 October 2016|url-status=live|archive-url=https://web.archive.org/web/20160925125914/http://www.iec.ch/si/binary.htm|archive-date=25 September 2016}}

The binary interpretation of metric prefixes is still prominently used by the Microsoft Windows operating system.{{cite web |url=http://support.microsoft.com/kb/121839 |title=Determining Actual Disk Size: Why 1.44 MB Should Be 1.40 MB |publisher=Support.microsoft.com |date=2003-05-06 |access-date=2014-03-25 |url-status=live |archive-url=https://web.archive.org/web/20140209012305/http://support.microsoft.com/kb/121839 |archive-date=2014-02-09 }} Binary interpretation is also used for random-access memory capacity, such as main memory and CPU cache size, due to the prevalent binary addressing of memory.

The binary meaning of the kilobyte for 1024 bytes typically uses the symbol KB, with an uppercase letter K. The B is sometimes omitted in informal use. For example, a processor with 65,536 bytes of cache memory might be said to have "64 K" of cache. In this convention, one thousand and twenty-four kilobytes (1024 KB) is equal to one megabyte (1 MB), where 1 MB is 1024² bytes.

In December 1998, the IEC addressed such multiple usages and definitions by creating prefixes such as kibi, mebi, gibi, etc., to unambiguously denote powers of 1024.{{cite web|url=http://physics.nist.gov/cuu/Units/binary.html|title=Prefixes for binary multiples|author=National Institute of Standards and Technology|author-link=National Institute of Standards and Technology|url-status=live|archive-url=https://web.archive.org/web/20070808000831/http://physics.nist.gov/cuu/Units/binary.html|archive-date=2007-08-08}} "In December 1998 the International Electrotechnical Commission (IEC) [...] approved as an IEC International Standard names and symbols for prefixes for binary multiples for use in the fields of data processing and data transmission." Thus the kibibyte, symbol KiB, represents 2¹⁰ bytes = 1024 bytes. These prefixes are now part of IEC 80000-13. The IEC further specified that the kilobyte should only be used to refer to 1000 bytes. The International System of Units restricts the use of the SI prefixes strictly to powers of 10.{{SIbrochure9th|page=143}}. "The SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The names and symbols for prefixes to be used with powers of 2 are recommended as follows: kibi Ki 2¹⁰ [...]"

• The Shugart SA-400 5{{1/4}}-inch floppy disk (1976) held 109,375 bytes unformatted,{{cite web |url=http://www.swtpc.com/mholley/SA400/SA400_Index.htm |title=SA400 minifloppy |publisher=Swtpc.com |date=2013-08-14 |access-date=2014-03-25 |url-status=dead |archive-url=https://web.archive.org/web/20140527094602/http://www.swtpc.com/mholley/SA400/SA400_Index.htm |archive-date=2014-05-27 }} and was advertised as "110 Kbyte", using the 1000 convention.{{cite web |url=http://www.swtpc.com/mholley/SA400/SA400_Datasheet.pdf |title=Shugart Associates SA 400 minifloppy TM Disk Drive |access-date=2011-06-24 |url-status=dead |archive-url=https://web.archive.org/web/20110608195322/http://www.swtpc.com/mholley/SA400/SA400_Datasheet.pdf |archive-date=2011-06-08 }} Likewise, the 8-inch DEC RX01 floppy (1975) held 256,256 bytes formatted, and was advertised as "256k".{{cite web |url=http://bitsavers.org/pdf/dec/disc/rx01/EK-RX01-MM-002_maint_Dec76.pdf |title=RXS/RX11 floppy disk system maintenance manual |access-date=2011-06-24 |url-status=dead |archive-url=https://web.archive.org/web/20110423194129/http://www.bitsavers.org/pdf/dec/disc/rx01/EK-RX01-MM-002_maint_Dec76.pdf |archive-date=2011-04-23 }} On the other hand, the Tandon 5{{1/4}}-inch DD floppy format (1978) held 368,640 (which is 360×1024) bytes, but was advertised as "360 KB", following the 1024 convention.
• Early home computer systems would often advertise using the 1024 convention, hence the naming of the Commodore 64, Commodore 128, and the Amstrad CPC 464.
• On modern systems, all versions of Microsoft Windows divide by 1024 and represent a 65,536-byte file as "64 KB". Conversely, Mac OS X Snow Leopard and newer represent this as 66 kB, rounding to the nearest 1000 bytes;{{cite web |url=http://support.apple.com/kb/TS2419 |title=How OS X and iOS report storage capacity |publisher=Support.apple.com |date=2013-07-01 |access-date=2014-03-25 |url-status=live |archive-url=https://web.archive.org/web/20140304015219/http://support.apple.com/kb/TS2419 |archive-date=2014-03-04 }} file sizes are reported with decimal prefixes.{{cite web |url=http://support.apple.com/kb/TS2419 |title=How Mac OS X reports drive capacity |publisher=Apple Inc |date=2009-08-27 |access-date=2009-10-16 |url-status=live |archive-url=https://web.archive.org/web/20091222235620/http://support.apple.com/kb/TS2419 |archive-date=2009-12-22 }}
• {{As of|2016|post=,}} the binary interpretation was still used in marketing and billing by some telecommunication companies, such as Vodafone,{{cite web|publisher=Vodafone Ireland|title=3G/GPRS data rates|url=https://www.vodafone.ie/planscosts_bus/data/|access-date=26 October 2016|url-status=live|archive-url=https://web.archive.org/web/20161026232743/https://www.vodafone.ie/planscosts_bus/data/|archive-date=26 October 2016}} AT&T,{{cite web |publisher=AT&T |title=Data Measurement Scale |url=http://www.att.com/support_static_files/KB/KB24648.html |access-date=26 October 2016 }}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }} Orange{{cite web|publisher=Orange Romania|title=Internet Mobile Access|url=https://www.orange.ro/recharge/internet.html|access-date=26 October 2016|url-status=dead|archive-url=https://web.archive.org/web/20161026234911/https://www.orange.ro/recharge/internet.html|archive-date=26 October 2016}} and Telstra.{{cite web|publisher=Telstra|title=Our Customer Terms|page=7|url=https://www.telstra.com.au/content/dam/tcom/personal/consumer-advice/pdf/intl-roaming.pdf|access-date=26 October 2016|url-status=live|archive-url=https://web.archive.org/web/20170410020355/https://www.telstra.com.au/content/dam/tcom/personal/consumer-advice/pdf/intl-roaming.pdf|archive-date=10 April 2017}}

• The Lord's Prayer, in Latin, is 296 bytes (about 0.3 kilobytes).{{cite web|title=Vulgata Clementina|url=http://www.sacredbible.org/articles/Matthew-Latin3.htm|quote=pater noster qui es in cælis sanctificetur nomen tuum adveniat regnum tuum fiat voluntas tua sicut in cælo et in terra panem nostrum supersubstantialem da nobis hodie et dimitte nobis debita nostra sicut et nos dimittimus debitoribus nostris et ne nos inducas in tentationem sed libera nos a malo|access-date=2024-02-29|archive-date=2022-12-05|archive-url=https://web.archive.org/web/20221205102852/https://sacredbible.org/articles/Matthew-Latin3.htm|url-status=live}}
• The short story The Cask of Amontillado by Edgar Allan Poe, hosted on Project Gutenberg as an uncompressed plain text file, is 12,843 bytes: this is 12.8 kilobytes (12,843 divided by 1,000) or 12.5 kibibytes (divided by 1,024).{{Cite web|url=https://www.gutenberg.org/files/25525/25525-h/25525-h.htm|title=The Cask of Amontillado|first=Edgar Allan|last=Poe|via=Project Gutenberg|access-date=2024-02-29|archive-date=2024-05-08|archive-url=https://web.archive.org/web/20240508202014/https://www.gutenberg.org/files/25525/25525-h/25525-h.htm|url-status=live}}
• The size of this article, as of April 2025, is about 14 kilobytes.

{{cols}}

• Binary prefix
• {{Section link|Gigabyte|Consumer confusion}}
• History of the floppy disk
• {{Section link|JEDEC memory standards|Unit prefixes for semiconductor storage capacity}}
• Timeline of binary prefixes
• {{Section link|Units of information|Size examples}}

{{colend}}

{{Reflist|30em}}

• {{cite web |url=http://www.jedec.org/sites/default/files/docs/JESD100B01.pdf |title=Terms, Definitions, and Letter Symbols for Microcomputers, Microprocessors, and Memory Integrated Circuits |date=December 2002 |publisher=JEDEC Solid State Technology Association |access-date=22 September 2013 |archive-date=13 March 2016 |archive-url=https://web.archive.org/web/20160313053915/http://www.jedec.org/sites/default/files/docs/jesd100b01.pdf |url-status=live }}

{{Computer Storage Volumes}}

Category:Units of information