Print shops ask for 300 DPI. Web guides say 72 DPI. Neither number means what most people think, and the confusion wastes gigabytes of upload bandwidth and whole photo orders. Here is the model that makes it all click.
PPI vs DPI vs megapixels
- Megapixels (MP): how many pixels a sensor or image contains. 24 MP = 24 million pixels. A property of the image itself.
- PPI (pixels per inch): pixel density of a screen. A property of the display.
- DPI (dots per inch): how many ink dots a printer lays down, several per pixel for color depth. A property of the printer.
The image file has no DPI until it is placed somewhere: the same 3000x2000 file is a 10-inch print at 300 PPI or a 31-inch print at 96 PPI. "DPI" embedded in a file is just a hint about intended print size.
How big can you print a photo?
| Camera | Megapixels | Max print @300 PPI | Poster @150 PPI |
|---|---|---|---|
| Phone (main lens) | 12 MP | 26 × 20 cm (10 × 8 in) | 51 × 39 cm (20 × 15 in) |
| Phone (48 MP mode) | 48 MP | 52 × 39 cm | 1.0 × 0.78 m |
| Entry DSLR | 24 MP | 51 × 34 cm | 1.0 × 0.68 m |
| High-res full frame | 61 MP | 81 × 54 cm | 1.6 × 1.1 m |
Viewing distance matters: posters are read from 1-2 m away, so 150 PPI is indistinguishable from 300 there. Billboards print at 15 PPI because nobody stands next to them.
Screen resolutions, translated
| Display | Pixels | Typical PPI |
|---|---|---|
| FHD monitor 24 in | 1920 × 1080 | 92 |
| 4K monitor 27 in | 3840 × 2160 | 163 |
| Laptop 14 in FHD | 1920 × 1080 | 157 |
| iPhone Pro | ~2800 × 1290 | 460 |
| 4K TV 55 in | 3840 × 2160 | 80 |
Web images: export at 2x the CSS display size for retina screens. A 600 CSS-px-wide hero wants a 1200-px file, saved as WebP/AVIF. Sending 3000-px files to the browser wastes 6x the bytes for zero visible gain.
The print-shop checklist
- Target print size in cm or inches
- Multiply by 300 (photo paper) or 150 (poster/canvas viewed at distance)
- That product = required pixels on the long edge
- Example: 20 × 30 cm poster at 150 PPI needs 1181 × 1772 px, a 2 MP image. Almost any camera delivers it
Convert inch dimensions precisely with cm ↔ inches.
The megapixel myth
After roughly 12 MP, more pixels mostly capture noise, not detail, unless the lens and sensor can resolve it. A 48 MP phone with a lens limited to 1.3 lines/pair/mm delivers about 12 MP of real detail; the rest is interpolation. Compare sensor size and lens quality, not the MP figure on the box. For printing decisions, the table above is the truth: even 12 MP prints beautifully to A3.
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