What are the common paper sizes?

The most common system of paper sizes in singapore is the ISO standard. Most people are familiar with the A series which includes A4 (highlighted on the chart) which is used everyday and the usual letterhead size. The C series is for envelopes - A C4 envelope being ideal for holding an A4 sheet. There is also a B series which provides intermediate sizes for the A series but this is rarely used.

A Paper Sizes B Paper Sizes C Paper Sizes 4A0 1682 × 2378 – – – – 2A0 1189 × 1682 – – – – A0 841 × 1189 B0 1000 × 1414 C0 917 × 1297 A1 594 × 841 B1 707 × 1000 C1 648 × 917 A2 420 × 594 B2 500 × 707 C2 458 × 648 A3 297 × 420 B3 353 × 500 C3 324 × 458 A4 210 × 297 B4 250 × 353 C4 229 × 324 A5 148 × 210 B5 176 × 250 C5 162 × 229 A6 105 × 148 B6 125 × 176 C6 114 × 162 A7 74 × 105 B7 88 × 125 C7 81 × 114 A8 52 × 74 B8 62 × 88 C8 57 × 81 A9 37 × 52 B9 44 × 62 C9 40 × 57 A10 26 × 37 B10 31 × 44 C10 28 × 40 All sizes are in millimetres

If you cut a sheet of A4 into two, the resulting halves are the same proportion as the original. In other words a sheet of A4 when folded in half gives you two sheets of A5. All A size papers have the same proportions. The largest sheet in this series is A0 which is 841mm x 1189mm and just happens to be one square metre in area (ISO paper sizes are rounded to the nearest millimetre).