Print guide
Print resolution explained: how many pixels does a sharp print need?
A customer hands you a photo and asks for an 8×10 print. Before you print, one simple sum tells you whether it will look sharp: pixels divided by inches.
The formula
PPI (pixels per inch) = pixels on one side ÷ inches on that side.
Do it for both the width and the height. If the photo and the print have different shapes, the two answers differ — the lower one is what you get when the photo fills the print, because the image is enlarged until the short side covers the paper.
To convert millimetres to inches, divide by 25.4.
Worked examples
| Photo | Print (filled) | Sum | Result |
|---|---|---|---|
| 4000 × 3000 px phone photo | 6 × 4 in | 3000 ÷ 4 = 750, 4000 ÷ 6 ≈ 667 | ≈ 667 PPI — plenty |
| 4000 × 3000 px | 18 × 12 in | 4000 ÷ 18 ≈ 222, 3000 ÷ 12 = 250 | ≈ 222 PPI — good |
| 1600 × 1200 px (compressed copy) | 10 × 8 in | 1600 ÷ 10 = 160, 1200 ÷ 8 = 150 | 150 PPI — borderline |
| 1600 × 1200 px | 18 × 12 in | 1600 ÷ 18 ≈ 89, 1200 ÷ 12 = 100 | ≈ 89 PPI — low |
The same photo can be perfect for a 6×4 and poor for a poster. Always check against the size actually being printed.
Rough thresholds
- 300 PPI or more: excellent for prints held in the hand.
- 200–299 PPI: good for most photo prints and frames.
- 150–199 PPI: acceptable for larger prints seen from a distance, such as wall frames and posters.
- Below 150 PPI: likely to look soft or blocky. Suggest a smaller size or ask for the original.
These are common guidelines, not hard rules. The printer, paper, viewing distance and the photo itself all matter.
What PPI cannot tell you
- Focus and shake. A blurred photo stays blurred at any PPI.
- Compression. A heavily compressed file can have enough pixels but blotchy detail — common with photos forwarded through chat apps.
- Upscaling. Enlarging a small file in software raises the pixel count but does not add real detail.
- Cropping. If the customer wants only one face from a group photo, the PPI is based on the cropped area, not the whole photo.
Where to find the pixel size
On a computer, open the file's properties or info panel (Windows: right-click → Properties → Details; Mac: Preview → Tools → Show Inspector). On a phone, most gallery apps show the resolution in the photo's details or info view. Check the file you will actually print, not the preview in a chat.