Short answer: the most common posters are A3 (29.7 × 42 cm) and A2 (42 × 59.4 cm) in Europe, and 18 × 24 in or 24 × 36 in in the US.
International (A-series) posters
| Size | cm | 150 DPI (px) |
|---|---|---|
| A4 | 21 × 29.7 | 1240 × 1754 |
| A3 | 29.7 × 42 | 1754 × 2480 |
| A2 | 42 × 59.4 | 2480 × 3508 |
| A1 | 59.4 × 84.1 | 3508 × 4967 |
| A0 | 84.1 × 118.9 | 4967 × 7022 |
US poster sizes
| Size (in) | cm | 150 DPI (px) |
|---|---|---|
| 11 × 17 (tabloid) | 27.9 × 43.2 | 1650 × 2550 |
| 18 × 24 | 45.7 × 61 | 2700 × 3600 |
| 24 × 36 | 61 × 91.4 | 3600 × 5400 |
| 27 × 40 (movie poster) | 68.6 × 101.6 | 4050 × 6000 |
Which DPI do posters need?
People look at posters from a distance, so 150 DPI is plenty for A3 and A2, and 100 DPI is usually fine for A1 and larger. Very large canvases slow down browsers — design at a smaller size with the same ratio, and let your print shop scale the PDF.