Backed by poular demand, and with a wish for everyone to be brought up to speed with the ever so interesting world of paper sizes I have wrote this section to explain the A sizing system.

Envelopes
Another Quick tip if you are buying envelopes you can fit an A size piece of paper in a corresponding C size envelope

Definition: 'A' size or 'A' series is a set of paper sizes established by the International Standards Organization (ISO) that ranges from 2A0 (the largest) to A7 (the smallest). The size of the paper goes down as the number goes up, and each is half the size of the previous e.g. two A4 sheets make up an A3 piece and two A5 sheets make up an A4 sheet.

'A' size -- size in millimetres -- approx inches
2A0 -- 1,189 x 1,682 mm -- 46.8 x 66.2 in
A0 -- 841 x 1,189 mm -- 33.1 x 46.8 in
A1 -- 594 x 841 mm -- 23.4 x 33.1 in
A2 -- 420 x 594 mm -- 16.5 x 23.4 in
A3 -- 297 x 420 mm -- 11.7 x 16.5 in
A4 -- 210 x 297 mm -- 8.3 x 11.7 in
A5 -- 148 x 210 mm -- 5.8 x 8.3 in
A6 -- 105 x 148 mm -- 4.1 x 5.8 in
A7 -- 74 x 105 mm -- 2.9 x 4.1 in

Hope this helps
Best wishes
Tim