A series paper sizes and dimensions are defined by the ISO 216 international paper size standard. The A series is comman and world wide used paper size. The base A0 size of paper is defined as having an area of 1 m2 and a dimension ratio of 1 to √2. Successive paper sizes in the series A1, A2, A3, and so forth, are defined by halving the preceding paper size across the larger dimension. This also effectively halves the area of each sheet. The most frequently used paper size is A4 measuring 210 by 297 millimetres (8.27 in × 11.7 in). The standard dimensions are rounded to the nearest millimetre.