A4

A4 is the most common paper size used internationally, defined by the ISO 216 standard. It measures 210 by 297 millimeters, with an aspect ratio of the square root of two, which allows it to be halved or doubled while preserving its proportions. This size is ubiquitous in office documents, personal printers, and official correspondence across the globe, forming the backbone of modern paper-based communication.

Standard paper size

A4 is the central size within the A series of the ISO 216 standard, which is maintained by the International Organization for Standardization. The defining principle of the series is that each size, from A0 to A10, is created by halving the preceding size along its longer dimension, resulting in all formats sharing the same √2:1 aspect ratio. This geometric property ensures that content can be scaled between sizes, such as from A3 to A4 or from A4 to A5, without cropping or distortion. The system is mathematically elegant and is complemented by the less common B series and C series, the latter used primarily for envelopes. The dimensions of A4 are precisely calculated from the area of an A0 sheet, which is defined as one square meter.

History and adoption

The concept of a standardized paper size with a constant aspect ratio has historical roots in the late 18th century, with principles outlined by the German scientist Georg Christoph Lichtenberg. However, the modern system was fully developed and instituted in the early 20th century by Walter Porstmann in Germany. It was formally adopted as the German industrial standard DIN 476 in 1922, a standard that would later form the basis for the international one. The adoption spread across Europe after World War II, gaining significant momentum. The system was officially codified as ISO 216 in 1975, leading to its near-universal adoption worldwide, with notable exceptions being the United States, Canada, and parts of Latin America, which primarily use the Letter size defined by ANSI/ASME Y14.1.

Technical specifications

An A4 sheet has exact dimensions of 210 millimeters in width and 297 millimeters in height, equivalent to 8.27 by 11.69 inches. Its area is 1/16 of a square meter, or approximately 0.0625 m². The √2:1 aspect ratio is key; when folded or cut in half parallel to its shorter sides, it yields two A5 sheets with identical proportions. This property is invaluable in printing and design workflows. For digital purposes, the standard dots per inch settings for A4 are integral to document creation in software like Adobe Acrobat and Microsoft Word. The paper density, or grammage, for common office use typically ranges from 80 g/m² to 100 g/m². The matching C4 envelope is designed to hold an unfolded A4 sheet.

International usage

A4 is the default paper size for business, administrative, and academic purposes in most countries, including all signatories to the ISO 216 standard. It is mandated for official government documents across the European Union, the United Kingdom, Australia, Japan, and South Africa, among many others. Its use is pervasive in laser printers, photocopiers, and notebooks sold globally. While North America predominantly uses the 8.5" x 11" Letter format, the ISO 216 system and A4 are still recognized and used within certain international business and scientific contexts, such as publications from IEEE and many academic journals. The global reach of A4 is a testament to the success of international standardization efforts.

Related paper sizes

Within the A series, A4 sits between the larger A3 (used for tabloids and diagrams) and the smaller A5 (common for notebooks and paperback books). The related B series, defined in ISO 216, includes sizes like B4 and B5, which are often used for book publishing and posters. The C series, such as C4 and C5, is specifically designed for envelopes to hold corresponding A-series paper without folding. Other regional standards exist alongside A4, most prominently the ANSI paper sizes (like Letter and Legal) in North America and the traditional Japanese B-series variant used in Japan.

Category:Paper sizes Category:ISO standards