Quick answer: divide the pixel width and height by the print resolution. At 300 pixels per inch (sharp, viewed up close) a 2400 × 3000 image prints at 8 × 10 inches. At 200 ppi (fine for wall prints viewed from a step back) the same file reaches 12 × 15 inches.
Print sizes for common pixel dimensions
| Pixels | At 300 ppi | At 200 ppi |
|---|---|---|
| 1200 × 1800 | 4 × 6 in | 6 × 9 in |
| 1500 × 2100 | 5 × 7 in | 7.5 × 10.5 in |
| 2400 × 3000 | 8 × 10 in | 12 × 15 in |
| 3300 × 4200 | 11 × 14 in | 16.5 × 21 in |
| 3550 × 4730 (about 17 MP) | about 11.8 × 15.8 in | about 17.7 × 23.6 in |
The last row is roughly the largest output Local Photo Upscaler produces. That comfortably covers 8 × 10 and 11 × 14 prints at full sharpness.
Working backwards from the print you want
Want a 5 × 7 at 300 ppi? You need about 1500 × 2100 pixels. With a 4× upscale, the source only has to be about 375 × 525. That is why upscaling works well for old small downloads, scans made at low resolution, and crops.
When a big print will still look soft
- The source was blurry. Upscaling enlarges blur along with everything else.
- The source was very small, such as a 100-pixel thumbnail. The model has too little to work with.
- Heavy JPEG compression. Blocky artifacts can turn into strange textures at print size. Try Denoise first.
Order a small test print before a large one, and view the result at 100% on screen first. Printers usually accept the saved file from Photos directly.