"A" series paper sizes

"A" series paper size format is defined by ISO 216 and is a perhaps the most popular paper size format in the world (with the exception of the US and Canada). The dimensions have an aspect ratio of 1:1.4142, and they double with each size (two A4 sheets form an A3, two A3 sheets form an A2, and so on)

"A" Size Millimeters Inches
A0 841 mm X 1189 mm 33.1" x 46.8"
A1 594 mm x 841 mm 23.4" x 33.1"
A2 420 mm x 594 mm 16.5" x 23.4"
A3 297 mm x 420 mm 11.7" x 16.5"
A4 210 mm x 297 mm 8.3" x 11.7"


Source: Wikipedia