The dimensions of the A series paper sizes are defined by the ISO 216 international paper size standard. The A series was adopted in Europe in the 19th century, and is currently used all around the world, apart from in the USA and Canada. The most common paper size used in English speaking countries around the world is A4, which is 210mm x 297mm (8.27 inches x 11.7 inches). The largest sheet from the A series is the A0 size of paper.
It has an area of 1m2, and the dimensions are 841mm x 1189mm. The A series uses an aspect ratio of 1:√2, and other sizes in the series are defined by folding the paper in half, parallel to its smaller sides. For example, cutting an A4 in half will create two A5 sheets, and so forth. Any size brochure can be made using paper from the next larger size, for example A3 sheets are folded to make A4 brochures. The standard lengths and widths of the A series are rounded to the nearest millimetre.