An A4 piece of paper measures 210 × 297 mm or 8.3 × 11.7 inches. Cutting it in half will create two A5 sheets of paper. An A4 piece of paper will fit into a C4 envelope. When folded in half, it will fit into a C5 envelope. A4 is part of the A series and is defined by the ISO 216 international paper size standard.