Understanding ISO A-series paper sizes
Every A-series sheet has the same shape. The ratio of long side to short side is always 1 : √2 (about 1.414), which has one very useful property: fold a sheet in half across its long side and you get exactly the next size down, with the proportions unchanged. That is why an A1 drawing photocopies onto A2 without leaving odd margins, and why scaling between sizes is always a clean factor.
The series is anchored on A0, which is defined as the sheet with an area of one square metre that has those proportions — 841 × 1189 mm. Halve it for A1, halve again for A2, and so on. Because each step halves the area, the linear dimensions shrink by a factor of √2 (roughly 71%) each time.
A-series dimensions at a glance
| Size | Millimetres | Centimetres | Inches | Typical use |
|---|
| A0 | 841 × 1189 | 84.1 × 118.9 | 33.1 × 46.8 | Full-size site and GA drawings |
| A1 | 594 × 841 | 59.4 × 84.1 | 23.4 × 33.1 | The standard architectural sheet |
| A2 | 420 × 594 | 42.0 × 59.4 | 16.5 × 23.4 | Detail drawings, smaller plans |
| A3 | 297 × 420 | 29.7 × 42.0 | 11.7 × 16.5 | Half-size prints, markups |
| A4 | 210 × 297 | 21.0 × 29.7 | 8.3 × 11.7 | Correspondence, schedules |
Which size are construction drawings usually on?
In the UK and across Europe, A1 is the default sheet for architectural and engineering drawings, with A0 used where a plan needs to be shown at 1:50 or 1:100 without splitting it across sheets. A2 and A3 turn up for details, sections and revision markups. If you have a roll of old drawings and are not sure what you are holding, measure the short edge: 594 mm is A1, 841 mm is A0.
A-series versus US ANSI sizes
North American drawings use the ANSI series instead, and the two are not interchangeable. ANSI D (22 × 34 in / 559 × 864 mm) sits between A1 and A2; ANSI E (34 × 44 in / 864 × 1118 mm) is close to, but smaller than, A0. Because the ANSI series does not preserve a constant aspect ratio, converting a drawing between the two systems always involves either a margin or a crop — something worth knowing before you send a US drawing to a UK print shop.
Why it matters for scanning and CAD conversion
Sheet size drives both cost and scan resolution. A larger sheet at the same DPI produces a much bigger file: doubling the area doubles the pixel count. Our scanning DPI calculator works out a sensible resolution for each size and estimates the resulting file, and the scale calculator converts between what you measure on the sheet and real-world dimensions. If you are having drawings digitised, knowing the sheet size is usually the first question you will be asked — our large format scanning service covers A0, A1 and A2 as standard.
Frequently asked questions