In the ISO paper size system, the height-to-width ratio of all pages is the square root of two (1.4142:1).
The width and the height of a page relate to each other like the side and the diagonal of a square. This aspect ratio is especially convenient for a paper size. If you put two such pages next to each other, or equivalently cut one parallel to its shorter side into two equal pieces, then the resulting page will have again the same width/height ratio.
ISO Sizes: A Series
The A series is commonly used for standard printing and stationary.
| ISO CODE | MILLIMETERS | INCHES | POINTS |
| 4A0 | 1682 x 2378 | 66.22 x 93.62 | 4768 x 6741 |
| 2A0 | 1189 x 1682 | 46.81 x 66.22 | 3370 x 4768 |
| A0 | 841 x 1189 | 33 x 46.81 | 2384 x 3370 |
| A1 | 594 x 841 | 23.39 x 33 | 1684 x 2384 |
| A2 | 420 x 594 | 16.54 x 23.39 | 1191 x 1684 |
| A3 | 297 x 420 | 11.69 x 16.54 | 842 x 1191 |
| A4 | 210 x 297 | 8.27 x 11.69 | 595 x 842 |
| A5 | 148 x 210 | 5.83 x 8.27 | 420 x 595 |
| A6 | 105 x 148 | 4.13 x 5.83 | 298 x 420 |
| A7 | 74 x 105 | 2.91 x 4.13 | 210 x 298 |
| A8 | 52 x 74 | 2.05 x 2.91 | 147 x 210 |
| A9 | 37 x 52 | 1.46 x 2.05 | 105 x 147 |
| A10 | 26 x 37 | 1.02 x 1.46 | 74 x 105 |
ISO Sizes: B Series
The B series is commonly used for wall charts, posters, etc.
| ISO CODE | MILLIMETERS | INCHES | POINTS |
| B0 | 1000 x 1414 | 39.37 x 55.67 | 2835 x 4008 |
| B1 | 707 x 1000 | 27.84 x 39.37 | 2004 x 2835 |
| B2 | 500 x 707 | 19.69 x 27.84 | 1417 x 2004 |
| B3 | 353 x 500 | 13.9 x 19.69 | 1001 x 1417 |
| B4 | 250 x 353 | 9.84 x 13.9 | 709 x 1001 |
| B5 | 176 x 250 | 6.93 x 9.84 | 499 x 709 |
| B6 | 125 x 176 | 4.92 x 6.93 | 354 x 499 |
| B7 | 88 x 125 | 3.47 x 4.92 | 249 x 354 |
| B8 | 62 x 88 | 2.44 x 3.47 | 176 x 249 |
| B9 | 44 x 62 | 1.73 x 2.44 | 125 x 176 |
| B10 | 31 x 44 | 1.22 x 1.73 | 88 x 125 |
ISO Sizes: C Series
The C series is commonly used for envelopes, as a C envelope is suitable to hold an A of the equivalent number value. The C series is also used for folders, postcard and envelopes.
| ISO CODE | MILLIMETERS | INCHES | POINTS |
| C0 | 917 x 1297 | 36.1 x 51.1 | 2599 x 3677 |
| C1 | 648 x 917 | 25.5 x 36.1 | 1837 x 2599 |
| C2 | 458 x 648 | 18.0 x 25.5 | 1298 x 1837 |
| C3 | 324 x 458 | 12.8 x 18.0 | 919 x 1298 |
| C4 | 229 x 324 | 9.0 x 12.8 | 649 x 919 |
| C5 | 162 x 229 | 6.4 x 9.0 | 459 x 649 |
| C6 | 114 x 162 | 4.5 x 6.4 | 323 x 459 |
| C7 | 114 x 81 | 3.2 x 4.5 | 230 x 323 |
| C8 | 57 x 81 | 2.2 x 3.2 | 162 x 230 |
| C9 | 40 x 57 | 1.6 x 2.2 | 113 x 162 |
| C10 | 28 x 40 | 1.1 x 1.6 | 79 x 113 |