The standard is based on a rectangle one square metre in area, the sides being in the ratio 1:square root of 2. The effect of this is that however many times the sheet is folded in half, the aspect ratio remains the same. Size A4 is one-sixteenth of A0 — 210mm × 297mm, or 8¼" × 11 2/3". There is a B series intermediate between A sizes: the dimensions of each size in millimetres are shown in the table:
A Series B Series
A0 841 × 1189 B0 1000 × 1414
A1 594 × 841 B1 707 × 1000
A2 420 × 594 B2 500 × 707
A3 297 × 420 B3 353 × 500
A4 210 × 297 B4 250 × 353
A5 148 × 210 B5 176 × 250
A6 105 × 148 B7 88 × 125
A8 52 × 74 B8 62 × 88
A9 37 × 52 B9 44 × 62
A10 26 × 37 B10 31 × 44
There is also a C series used for envelopes, with dimensions as follows:
C4 324 × 229
C5 229 × 162
C6 114 × 162
When buying paper for your word processor you should be aware that some continuous stationery for computer use is supplied in 11" sheets, rather than the A4 size of 11 2/3". Take care that the paper length setting in your word processor matches the length of paper you are using; otherwise, you will find that after printing a few pages, your text no longer lines up correctly.It may also be necessary to adjust the setting of your printer.