The range of sizes in the ISO A-Series for drawing papers is based on a rectangle of area one square metre, the sides of which are in the proportion 1: √ 2 (this ratio is distinct from the 'golden section', which has a different basis). Smaller sheets in the series are derived by successively halving them and rounding the dimensions up or down to whole numbers. The ratio of the lengths of the sides remains approximately the same throughout, e.g.

The trimmed sizes of drawing sheets given in BS 3429 are shown in the table below. They are in millimetres with approximate imperial equivalents (inches) in parenthesis. Approximate areas are in square metres with imperial equivalents (square feet) in parenthesis.

A# | Length | Width | Area |

A0 | 841 (33.11) | 1189 (46.81) | 1.0 (10.76) |

A1 | 594 (23.39) | 841 (33.11) | 0.5 (5.38) |

A2 | 420 (16.54) | 594 (23.39) | 0.25 (2.69) |

A3 | 297 (11.69) | 420 (16.54) | 0.125 (1.34) |

A4 | 210 (8.27) | 297 (11.69) | 0.062 (0.67) |

A5 | 148 (5.83) | 210 (8.27) | 0.031 (0.33) |