Each is half the area of the one before, ie A4 paper (297 mm × 210 mm) is half the size of A3 paper (297 mm × 420 mm).

International A series paper size formats from A0 to A10, including the most popular A3, A4 and A5 formats. International A series paper size formats from A0 to A10, including the most popular A3, A4 ...

This is an on-paper comparison taking into account manufacturer ... This comparison focuses on the core A3 and A4 ranges, not the performance-focused S- and RS-badged derivatives.