A Paper Sizes

The ISO 216 international standard defines the dimensions of the A series of paper sizes, which have been widely adopted around the world except in North America. The A series uses an aspect ratio of 1:√2. The largest size A0 has dimensions of 841mm x 1189mm and an area of 1 square meter. Other sizes in the series are defined by folding the paper in half parallel to the shorter sides, so each successive size is half the area of the previous one. For example, A4 paper, the most commonly used size worldwide, is 210mm x 297mm and can be cut from A3 paper. The A series allows efficient scaling and folding of paper for uses like photocopying and making brochures. The dimensions are rounded to the nearest millimeter.