The one formula you need
Pixels needed = print size in inches × ppi. An 8 × 10 inch print at 300 ppi needs 2400 × 3000 pixels. For centimetres, divide by 2.54 first. The upscale factor is the pixels needed divided by the pixels you have, on whichever side is the tighter fit.
Pixels needed for common print sizes
| Print size | 300 ppi | 200 ppi | 150 ppi |
|---|---|---|---|
| 4 × 6 in | 1200 × 1800 | 800 × 1200 | 600 × 900 |
| 5 × 7 in | 1500 × 2100 | 1000 × 1400 | 750 × 1050 |
| 8 × 10 in | 2400 × 3000 | 1600 × 2000 | 1200 × 1500 |
| A4 (210 × 297 mm) | 2480 × 3508 | 1654 × 2339 | 1240 × 1754 |
| 11 × 14 in | 3300 × 4200 | 2200 × 2800 | 1650 × 2100 |
| A3 (297 × 420 mm) | 3508 × 4961 | 2339 × 3307 | 1754 × 2480 |
| 16 × 20 in | 4800 × 6000 | 3200 × 4000 | 2400 × 3000 |
| A2 (420 × 594 mm) | 4961 × 7016 | 3307 × 4677 | 2480 × 3508 |
| 24 × 36 in | 7200 × 10800 | 4800 × 7200 | 3600 × 5400 |
Calculated values, rounded to the nearest pixel. Use the print size calculator for your own image and sizes.
Viewing distance changes everything
Someone with normal (20/20) vision resolves about one arcminute. That works out to roughly 3438 ÷ viewing distance in inches pixels per inch before extra pixels stop being visible. At reading distance (12 in) that’s about 290 ppi, which is where the 300 ppi rule comes from. At 3 feet it’s about 95 ppi, and at 6 feet about 48 ppi.
| Viewed from | Acuity limit | Practical target |
|---|---|---|
| 30 cm / 12 in (hand-held) | ≈ 286 ppi | 300 ppi |
| 60 cm / 24 in (desk, small frame) | ≈ 143 ppi | 150–200 ppi |
| 1 m / 39 in (wall print) | ≈ 87 ppi | 100–150 ppi |
| 3 m / 10 ft (poster, banner) | ≈ 29 ppi | 50–75 ppi |
Acuity limit = 1 ÷ (distance × tan(1/60°)). This is a rule of thumb. Viewers walk up to prints, so leave some margin.
Workflow
- Crop to the print’s aspect ratio first (8 × 10 is 4:5; A sizes are 1:√2). Otherwise you upscale pixels you’ll throw away.
- Calculate the target pixels for the print size and viewing distance.
- Upscale once, straight to that size, with a faithful model for photos or a creative one for AI art. Chaining 2× passes builds up artefacts.
- Sharpen for output lightly at the final size. Matte paper needs a little more than gloss.
- Export as the format the lab asks for (usually high-quality JPEG or TIFF) in sRGB, unless the lab gives you an ICC profile.
Selling prints made from AI art? Upsampler has notes on preparing print-on-demand files.
FAQ
Do I really need 300 dpi?
300 ppi is the right target for photos viewed in the hand: prints, photo books, flyers. Wall prints seen from a metre or more look just as sharp at 150–200 ppi, and large posters or banners viewed from across a room are often printed at 100 ppi or less. The calculator works this out from the viewing distance.
What’s the difference between DPI and PPI?
PPI (pixels per inch) describes the image: how many of its pixels land on each inch of paper. DPI (dots per inch) describes the printer: how many ink dots it lays down. People use “300 dpi” loosely to mean 300 ppi. The DPI number stored in a file’s metadata doesn’t change the pixels at all.
Should I upscale myself or let the print lab do it?
Labs usually resample with a simple algorithm. If your file is short of the pixels you need, an AI upscale to the exact print size, made by you, usually looks better than the lab’s resize. Send the lab exactly the pixel dimensions its template asks for.