Editing Paper size (section)

{{Short description|Standard sizes of paper}}
{{For|sizing as the ingredient used in papermaking|Sizing#Papermaking}}
{{Use British English |date=January 2024}}
{{Use dmy dates|date=September 2021|cs1-dates=y}}
[[File:PapierformateA0bisA8.jpg|thumb|Paper sizes A0 to A8, life-size installation ''The Invasion of the Square Roots'' at the [[CosmoCaixa Barcelona]] science museum]]
[[File:A size illustration2 with letter and legal.svg|thumb|right|A size chart illustrating the ISO A series and a comparison with American letter and legal formats]]
[[File:Comparison paper sizes.svg|thumb|Comparison of some paper and photographic paper sizes close to the A4 size]]

'''Paper size''' refers to [[Technical standard|standardized]] dimensions for sheets of paper used globally in [[stationery]], [[printing]], and [[technical drawing]]. Most countries adhere to the [[ISO 216]] standard, which includes the widely recognized A series (including [[A4 paper]]), defined by a consistent aspect ratio of √2. The system, first proposed in the 18th century and formalized in 1975, allows scaling between sizes without distortion. Regional variations exist, such as the [[#North American paper sizes|North American paper sizes]] (e.g., [[Letter (paper size)|Letter]], [[Legal paper|Legal]], and [[Ledger paper|Ledger]]) which are governed by the [[American National Standards Institute|ANSI]] and are used in North America and parts of Central and South America.<ref name="CLDR"/>

The standardization of paper sizes emerged from practical needs for efficiency. The ISO 216 system originated in late-18th-century Germany as [[Deutsches Institut für Normung|DIN]] 476, later adopted internationally for its mathematical precision. The origins of North American sizes are lost in tradition and not well documented, although the Letter size ({{cvt|8.5|×|11|in}}) became dominant in the US and Canada due to historical trade practices and governmental adoption in the 20th century. Other historical systems, such as the British ''Foolscap'' and Imperial sizes, have largely been phased out in favour of ISO or ANSI standards.

Regional preferences reflect cultural and industrial legacies. In addition to ISO and ANSI standards, Japan uses its [[Japanese Industrial Standards|JIS]] P 0138 system, which closely aligns with ISO 216 but includes unique B-series variants commonly used for books and posters. Specialized industries also employ non-standard sizes: [[newspaper]]s use custom formats like [[Berliner (format)|Berliner]] and [[broadsheet]], while [[envelope]]s and [[business card]]s follow distinct sizing conventions. The international standard for envelopes is the [[#ISO C|C series]] of [[ISO 269]].