A3

The A3 paper size is part of the A series formats defined in the ISO 216 standard. With dimensions of 297 mm x 420 mm, the A3 sheet has an area of 0.125 square meters, half the area of an A2 sheet. The A3 size was developed as part of the A series based on the aspect ratio of √2, enabling the paper sizes to neatly scale down when folded in half.

The origins of A3 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 A3 format itself was formalized in the early 20th century German standards that led to the international standardization of the A series and A3 in 1975. Today, the A3 format is often used for posters, charts, presentations, and drawings. It also serves as a starting point to make booklets, brochures, and flyers in A4 when folded in half. Its dimensions make A3 a versatile option for both office and personal uses.