A3 paper size
297 × 420 mm
11.69 × 16.54 inches · 29.7 × 42 cm · aspect ratio 1:1.41
A3 size is 297 × 420 mm. Those are the A3 dimensions a printer works to; the same sheet in centimetres, inches, points and pixels is below.
What A3 is for
A3 is exactly two A4 sheets side by side, and it is the largest size most office printers will take — which makes it the practical ceiling for anything printed in-house. Spreadsheets that will not fit A4 legibly, engineering drawings, and small posters all end up here. Its North American near-equivalent is Tabloid at 279 × 432 mm, which is close enough to look interchangeable and different enough that a design laid out for one will be rescaled by the driver when printed on the other.
A3 dimensions in every unit
| Unit | Width | Height |
|---|---|---|
| Millimetres | 297 mm | 420 mm |
| Centimetres | 29.7 cm | 42 cm |
| Inches | 11.69 in | 16.54 in |
| Points (PostScript) | 842 pt | 1191 pt |
A3 in pixels
Pixel dimensions depend entirely on the resolution you are working at — there is no single "pixel size" for a sheet of paper. A3 size in pixels has every resolution, with file sizes and canvas setup.
| Resolution | Pixels | Use |
|---|---|---|
| 72 DPI | 842 × 1191 | Screen preview only — far too coarse to print |
| 150 DPI | 1754 × 2480 | Draft printing, internal documents |
| 300 DPI | 3508 × 4961 | The standard for commercial print |
| 600 DPI | 7016 × 9921 | Fine detail, line art, archival scanning |
Setting up a print document? Use 300 DPI and add 3 mm of bleed on every edge unless your printer specifies otherwise.
How A3 relates to the rest of the series
A3 is A0 halved 3 times. Halving a sheet across its longer side is what generates the next size down, and because the sides are in a 1:√2 ratio the proportions survive every fold — which is the entire reason the series exists.
That makes 8 sheets of A3 exactly one sheet of A0, with nothing left over. The area works out at 0.125 m², since A0 is defined as one square metre.
Against the sheet most people picture: one of these holds 2 A4 sheets.
Scaling to the next size up or down is a factor of √2 ≈ 1.414 on each edge, so enlarging A3 to the next size is 141% on a photocopier and reducing it is 71%. Those two numbers are on the preset buttons of most copiers for exactly this reason, and they are the same for every size in the series.
About A3
Exactly two A4 sheets side by side. The largest size most office printers handle, and the standard for spreadsheets, drawings and small posters.
Why A sizes halve so neatly
The A series is built on a 1:√2 ratio — approximately 1:1.414. That proportion has a unique property: cut the sheet in half across its long side and the two halves keep exactly the same proportions. This is why two A4 sheets make an A3, why scaling A4 artwork to A3 needs no cropping, and why photocopiers have a single "A4 → A3" button that just works.
Other ISO A series sizes
| Size | Millimetres | Inches |
|---|---|---|
| A0 | 841 × 1189 mm | 33.11 × 46.81 in |
| A1 | 594 × 841 mm | 23.39 × 33.11 in |
| A2 | 420 × 594 mm | 16.54 × 23.39 in |
| A4 | 210 × 297 mm | 8.27 × 11.69 in |
| A5 | 148 × 210 mm | 5.83 × 8.27 in |
| A6 | 105 × 148 mm | 4.13 × 5.83 in |
| A7 | 74 × 105 mm | 2.91 × 4.13 in |
| A8 | 52 × 74 mm | 2.05 × 2.91 in |
| A9 | 37 × 52 mm | 1.46 × 2.05 in |
| A10 | 26 × 37 mm | 1.02 × 1.46 in |
| Super A3 | 329 × 483 mm | 12.95 × 19.02 in |
Frequently asked questions
What size is A3 in mm?
297 × 420 mm.
What size is A3 in inches?
11.69 × 16.54 inches.
What size is A3 in pixels?
There is no single answer — it depends on resolution. At the print standard of 300 DPI it is 3508 × 4961 pixels; at 72 DPI it is only 842 × 1191.