A4

The A4 paper size is part of the A series formats defined in the ISO 216 standard. With dimensions of 210 mm x 297 mm, the A4 sheet has an area of 0.0625 square meters. The A4 size was developed as part of the A series based on the aspect ratio of √2, enabling each size to neatly fold down from the larger sheets.

The origins of A4 date back to the late 18th century in Germany along with the other A series sizes. The √2 aspect ratio was first proposed in a 1786 letter by German scientist Georg Christoph Lichtenberg. This geometric ratio allowed for the creation of the A series with its ability to smoothly scale sizes up and down by folding sheets in half. The A4 format itself was formalized in the early 20th century German standards that led to the international standardization of the A series and A4 in 1975. Today, A4 is the most commonly used paper size worldwide for office and personal use. Its versatility for printing and copying makes A4 a practical choice for everything from letters to invoices to brochures.