ISO A SERIES PAPER SIZES
Successive paper sizes in the series A1, A2, A3, and so forth, are defined by halving the preceding paper size along the larger dimension. The most frequently used paper size is A4 (210 × 297 mm) and by halving the larger dimension (297 mm) the size becomes A5 and so on.
A0 841x1189mm / A1 594x840mm / A2 420x594mm
A3 297x420mm / A4 210x297mm / A5 148x210mm
A6 105x148mm / A7 74x105mm / A8 52x74mm