Sizes of drawings typically comply with either of two different standards, ISO (World Standard) or U.S. customary, according to the following tables:| A4 | 210 X 297 |
|---|---|
| A3 | 297 X 420 |
| A2 | 420 X 594 |
| A1 | 594 X 841 |
| A0 | 841 X 1189 |
| A | 8.5" X 11" |
|---|---|
| B | 11" X 17" |
| C | 17" X 22" |
| D | 22" X 34" |
| E | 34" X 44" |
| D1 | 24" X 36" |
|---|---|
| E1 | 30" X 42" |
The metric drawing sizes correspond to international paper sizes. These developed further refinements in the second half of the twentieth century, when photocopying became cheap. Engineering drawings could be readily doubled (or halved) in size and put on the next larger (or, respectively, smaller) size of paper with no waste of space. And the metric technical pens were chosen in sizes so that one could add detail or drafting changes with a pen width changing by approximately a factor of the square root of 2. A full set of pens would have the following nib sizes: 0.13, 0.18, 0.25, 0.35, 0.5, 0.7, 1.0, 1.5, and 2.0 mm. However, the International Organization for Standardization (ISO) called for four pen widths and set a colour code for each: 0.25 (white), 0.35 (yellow), 0.5 (brown), 0.7 (blue); these nibs produced lines that related to various text character heights and the ISO paper sizes.
All ISO paper sizes have the same aspect ratio, one to the square root of 2, meaning that a document designed for any given size can be enlarged or reduced to any other size and will fit perfectly. Given this ease of changing sizes, it is of course common to copy or print a given document on different sizes of paper, especially within a series, e.g. a drawing on A3 may be enlarged to A2 or reduced to A4.
The U.S. customary "A-size" corresponds to "letter" size, and "B-size" corresponds to "ledger" or "tabloid" size. There were also once British paper sizes, which went by names rather than alphanumeric designations.
American National Standards Institute (ANSI) Y14.2, Y14.3, and Y14.5 are standards that are commonly used in the U.S.
