ISO Paper sizes - A brief overview
To define paper sizes, the most common and more or less universally adopted system in Europe, is the ISO standard.
An in-depth article on the ISO system for paper sizes can be found here. In particular, the article summarises standards adopted internationally and where they deviate from the system which is now accepted in the UK. In the outline which follows, we describe briefly the ISO paper size system and it's importance.
The key to the ISO system is to be found in the use of the square root of 2 to define the aspect ratio of each paper (or card) sheet size. Thus the ratio of width to height is 1:1.414. This gives the series the unique property - if you cut any sheet into 2 equal halves you will have sheets of the next size down in the series. For example, an A4 sheet cut into 2 yields 2 A5 sheets.
All "A" size papers have the same proportions. The largest sheet in the "A" series is A0 which is 841mm x 1189mm - actually and interestingly one square metre in area (ISO paper sizes are rounded to the nearest millimetre).
Paper sizes - The ISO system
Here are the sizes in millimeters of each sheet size in the ISO system:
| A | B | C | RA | SRA | |
| 0 | 841 x 1189 | 1000 x 141 | 917 x 1296 | 860 x 1220 | 900 x 1280 |
| 1 | 594 x 841 | 707 x 1000 | 648 x 917 | 610 x 860 | 640 x 900 |
| 2 | 420 x 594 | 500 x 700 | 458 x 648 | 430 x 610 | 450 x 640 |
| 3 | 297 x 420 | 353 x 500 | 324 x 458 | 305 x 430 | 320 x 450 |
| 4 | 210 x 297 | 250 x 353 | 229 x 324 | 215 x 305 | 225 x 320 |
| 5 | 148 x 210 | 176 x 250 | 162 x 229 | 152 x 215 | 160 x 225 |
| 6 | 105 x 148 | 125 x 176 | 114 x 162 | 107 x 152 | 112 x 160 |
| 7 | 74 x 105 | 88 x 125 | 81 x 114 | 76 x 107 | 80 x 112 |
| 8 | 52 x 74 | 62 x 88 | 57 x 81 | 53 x 76 | 56 x 80 |
In addition to the "A" series which includes the A4 size used for standard letterheads, there is the "C" series for envelopes (A C4 envelope is ideal for holding an A4 sheet unfolded) and also a "B" series which provides intermediate but in fact rarely used sizes for the "A" series. DL is the special size which applies to envelopes designed to accept A4 paper folded in three.
Two other series which are also important for the Print for Pay industry are the "RA" and "SRA" series (Raw and Supplementary Raw) . As seen in the chart, these are slightly larger than the "A" series to make allowances for grip, trimming and bleed (ie: for situations where the finished item is to have print right to the edge of the sheet. Typically an extra 3mm is allowed by designers to allow leeway when trimming to standard "A"sizes).
Paper handling and the ISO system
The advantage of an unqualified agreement on paper standard enables photocopier and multifunctional printer/copiers manufacturers to develop and improve their systems for all common paper handling and copying tasks. For many years, photocopier systems have had predefined function keys to enable enlarged or reduced copy / print output from any original, without unnecessary waste from experimentation. These days such functions appear in visually exciting, user-friendly LCD displays.
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