At a strict 300 PPI a 24×36 inch print would need 7200 × 10800 pixels (77.8 megapixels) — more than most cameras produce. In practice, posters are viewed from several feet away, so 150–200 PPI usually looks sharp.
| Resolution | Pixels needed | Megapixels | Quality |
|---|---|---|---|
| 300 PPI | 7200 × 10800 px | 77.8 MP | Excellent — close viewing |
| 200 PPI | 4800 × 7200 px | 34.6 MP | Good — normal distance |
| 150 PPI | 3600 × 5400 px | 19.4 MP | Acceptable — wall viewing |
The maths is print inches × PPI for each side: 24 in × 300 = 7200 px and 36 in × 300 = 10800 px, and 7200 × 10800 = 77,760,000 pixels = 77.76 megapixels (rounded to 77.8 MP above).
24×36 is a 2:3 aspect ratio — the same shape as a standard 3:2 camera sensor, so most camera photos fill the sheet with no crop. The key variable is viewing distance. The eye can only resolve a limited amount of detail, and that limit falls as you step back:
Example: a common 6000 × 4000 px photo (24 MP) gives about 167 PPI at this size — 6000 ÷ 36 = 167 on the long side and 4000 ÷ 24 = 167 on the short side — above the 150 PPI poster threshold, so it is a realistic poster candidate, not a failure for missing 300 PPI.