ISO 216 · A-series
A3 paper size
A3 measures 297 × 420 mm — twice the area of A4 and large enough to be useful as a small poster, a double-page spread, or for technical drawings and architectural prints. Most home printers cannot handle A3, but it is standard in copy shops and design studios.
Exact dimensions
Image sizes for full-page raster content are listed at every common DPI value. For commercial offset and digital print, target 300 DPI; for large-format print viewed from a distance, 150 DPI is often acceptable.
| Unit | Width | Height |
|---|---|---|
| Millimetres (mm) | 297 | 420 |
| Centimetres (cm) | 29.7 | 42 |
| Inches (in) | 11.693 | 16.535 |
| Pixels @ 72 DPI | 842 | 1,191 |
| Pixels @ 96 DPI | 1,123 | 1,587 |
| Pixels @ 150 DPI | 1,754 | 2,480 |
| Pixels @ 200 DPI | 2,339 | 3,307 |
| Pixels @ 300 DPI | 3,508 | 4,961 |
| Pixels @ 600 DPI | 7,016 | 9,921 |
A3 — 297 × 420 mm
Where A3 is used
- · Small posters and event signage
- · Architectural and engineering drawings
- · Magazine and newspaper double-page spreads
- · Wall calendars and pin-up planners
- · Mood boards and design layouts
- · Children's drawing pads
Print resolution at A3 scale
Because A3 is twice the area of A4, a raster image that looks sharp at A4 will look softer when scaled up. If you plan to print at A3, source or generate images at A3 dimensions from the start. A 300 DPI A3 image is 3508 × 4961 pixels — about 17.4 megapixels.
For text and vector graphics this does not apply: vectors scale losslessly.
Designing posters at A3
Bleed: 3–5 mm
For full-bleed A3 posters, extend the artwork 3 mm past every edge (5 mm if your printer recommends it). The full export size becomes 303 × 426 mm or 307 × 430 mm respectively.
Readable type sizes
For a poster read from 1–2 m away, headings should be at least 36 pt and body text at least 14 pt. The "viewing distance × 0.005" rule of thumb gives a useful minimum cap-height in cm.
Safe area: 5 mm inside the trim
Keep all critical text and logos at least 5 mm in from the trim line to avoid losing detail at the cutting stage.
Export format
PDF/X-1a is the safest commercial-print format. It flattens transparency, embeds fonts and fixes the page size, which prevents most production-time surprises.
Frequently asked questions
What are the exact dimensions of A3?
A3 is 297 × 420 millimetres, which is 29.7 × 42.0 centimetres, or approximately 11.69 × 16.54 inches.
Is A3 twice the size of A4?
Yes. A3 has exactly twice the area of A4: two A4 sheets placed side by side equal one A3 sheet. The 1 : √2 aspect ratio is preserved.
Can a normal home printer print A3?
Most home printers max out at A4 or US Letter. A3 usually requires a wide-format printer, which is more common in offices, copy shops and design studios. Online print services accept A3 PDFs as standard.
How many pixels is A3 at 300 DPI?
At 300 DPI, A3 is 3508 × 4961 pixels. That is the minimum image resolution for a full-page raster image intended for commercial print.
When should I use A3 instead of A4?
Use A3 when content cannot fit comfortably on A4, when you need a small poster, for double-page spreads, for technical drawings that need detail, or when presenting data tables that would otherwise wrap awkwardly.