The 'A' series is the standard paper size defined by the International Standards Organization and is used among all countries that use the metric system - every country but the U.S.
The sizes for the 'A' series are as follows (HxW):
A0 = 1189 x 841 mm A1 = 841 x 594 mm A2 = 594 x 420 mm A3 = 420 x 297 mm A4 = 297 x 210 mm (up to A10 - see chart below);
or in inches:
A0 = 46.8 x 33.1 in A1 = 33.1 x 23.4 in A2 = 23.4 x 16.5 in A3 = 16.5 x 11.7 in A4 = 11.7 x 8.3 in (up to A10 - see chart below);