What size is A3 paper?

Answer 1

The A series paper has a height to width ratio of square root 2 to 1 (1.4142:1)

A sheet of A0 has an area of one square metre. To fit the ratio its sides are 841 millimetre x 1189 millimetre.

Each sheet in the series is half the size of the previous sheet; the height of A1 would be the width of A0, the width of A1 is half the height of A0, 594 mm x 841 mm.

A3 has a height of 420 millimetres and a width of 297 millimetres.

Answer 2

An A3 sheet paper its twice the size of an A4 sheet of paper. An A3 sheet of paper measures:

297mm × 420mm or 11.69'' × 16.54''