Applying the 300 DPI print standard to a large poster produces an absurd requirement: an A0 poster at 300 DPI needs roughly 9933 × 14043 pixels — 140 megapixels. Almost nobody has that, and almost nobody needs it.
Resolution Depends on Viewing Distance
Your eye resolves a fixed *angle*, not a fixed number of dots. The further away something is viewed, the fewer dots per inch it needs:
- Held in hand (25–30 cm) — 300 DPI. Photo prints, brochures, business cards.
- Viewed at arm's length to 1 m — 200 DPI is comfortable. Small posters, presentation boards.
- 1–3 m — 150 DPI. Typical wall posters.
- 3–10 m — 100 DPI or less. Large-format posters, exhibition graphics.
- Billboards (tens of metres) — 10–20 DPI is normal. Printed billboard files are often only a few thousand pixels wide.
The Pixel Table
At 150 DPI, a practical standard for a poster viewed from a metre or two:
| Size | Millimetres | Pixels at 150 DPI |
|---|---|---|
| A3 | 297 × 420 | 1754 × 2480 |
| A2 | 420 × 594 | 2480 × 3508 |
| A1 | 594 × 841 | 3508 × 4967 |
| A0 | 841 × 1189 | 4967 × 7022 |
At 200 DPI multiply by 1.33; at 100 DPI multiply by 0.67. The formula is always millimetres ÷ 25.4 × DPI.
What Matters More Than DPI
- Sharpness of the source. A genuinely sharp 3000 px photo prints better at A1 than a soft 6000 px one. Camera shake and missed focus can't be fixed by resolution.
- Compression artifacts scale up too. A heavily compressed JPEG shows its blocks at poster size. Work from originals.
- Type is different from photos. Text and vector graphics should always be vector in the final file — they print at the device's full resolution regardless of the image DPI. Never rasterize headline type into a 150 DPI image.
- Paper and finish. Uncoated stock absorbs ink and softens detail, so extra resolution is wasted on it; glossy paper shows more.
If Your File Is Too Small
- Check the actual required DPI with the printer for the intended viewing distance — you may already be fine.
- Reduce the print size to what the pixels support.
- Use a quality upscaler to reach the target; modern upscaling handles moderate enlargement (up to about 2×) well, especially for images without fine text.
- Change the design: crop tighter, use the photo as a background element with a colour overlay, or build a type-led poster where the image is secondary.
- Reshoot if it matters and you can.
Before Sending
Ask the printer for their required DPI, colour profile and file format. Set up bleed and safe margins, embed or outline fonts, and send a PDF unless told otherwise. Their spec beats any general rule, including this article's.