ISO Paper Sizes
The paper formats defined by ISO in the A, B and C series are used today in nearly all countries apart from North America.
The formats have been determined according to the following rules:
- A0 has an area of one square meter.
- The aspect ratio of all members of the A, B and C-series is sqrt(2) = 1.41421...
- You get the next higher format by cutting the paper in two equal pieces parallel to the shorter side. This results again in a 1 : sqrt(2) format (that's the big advantage of this format).
- The size of a B-series paper is the geometric mean between the size of the corresponding A-series paper and the next bigger A-series paper.For example, B1 is between A1 and A0.
- The size of a C-series paper is the geometric mean between the size of the A-series and B-series paper with the same number.
This means that the following formulas give the dimensions in meters:
| Paper Size | Width | Height |
| A-series | 2 ^ (- 1/4 - n/2) | 2 ^ (1/4 - n/2) |
| B-series | 2 ^ ( - n/2) | 2 ^ (1/2 - n/2) |
| C-series | 2 ^ (- 1/8 - n/2) | 2 ^ (3/8 - n/2) |
Larger sizes have smaller numbers. Sizes larger than those with n = 0 are written as 2 A0 and 4 A0 rather than A(-1) and A(-2).
The following table lists the official definitions of the paper sizes which are the values from the above formulas rounded more-or-less to an integral number of millimeters:
| Paper Size | Dimension
(millimeters) | Paper Size | Dimension
(millimeters) | Paper Size | Dimension
(millimeters) |
| 4 A0 | 1682 x 2378 | B0 | 1000 x 1414 | C0 | 917 x 1297 |
| 2 A0 | 1189 x 1682 |
| A0 | 841 x 1189 |
| A1 | 594 x 841 | B1 | 707 x 1000 | C1 | 648 x 917 |
| A2 | 420 x 594 | B2 | 500 x 707 | C2 | 458 x 648 |
| A3 | 297 x 420 | B3 | 353 x 500 | C3 | 324 x 458 |
| A4 | 210 x 297 | B4 | 250 x 353 | C4 | 229 x 324 |
| A5 | 148 x 210 | B5 | 176 x 250 | C5 | 162 x 229 |
| A6 | 105 x 148 | B6 | 125 x 176 | C6 | 114 x 162 |
| A7 | 74 x 105 | B7 | 88 x 125 | C7 | 81 x 114 |
| A8 | 52 x 74 | B8 | 62 x 88 | C8 | 57 x 81 |
| A9 | 37 x 52 | B9 | 44 x 62 | C9 | 40 x 57 |
| A10 | 26 x 37 | B10 | 31 x 44 | C10 | 28 x 40 |
Some of the more popular sizes:
| Size | Purpose |
| A0 | technical drawings |
| A4 | letters, magazines, documents |
| A5 | books |
| C4, C5, C6 | envelopes |
| B4, A3 | supported by many copy machines, newspapers |
There are also strip formats possible, for example:
| Size | Dimensions |
| 1/3 A4 | 99 x 210 |
| 2/3 A4 | 198 x 210 |
| 1/4 A4 | 74 x 210 |
| 1/8 A4 | 37 x 210 |
| 1/4 A3 | 105 x 297 |
| 1/3 A5 | 70 x 148 |
All these formats are paper end formats. In other words, these are the dimensions of the paper delivered to the user/reader. Other standards define slightly bigger paper sizes for applications where the paper will be cut to the end format later (for example, after binding).
The ISO DL envelope format has the dimensions 220 x 110 millimeters.