- a series of paper sizes approved by the International Standards Organization, running from 2AO to A7, each size (defined in mm) being half as large as the one preceding it, as follows: 2AO,1189 × 1682; AO, 841 × 1189; A1, 594 × 841; A2, 420 × 594; A3, 297 × 420; A4, 210 × 297; A5, 148 × 210; A6, 105 × 148; A7, 74 × 105
