Pixels, PPI and DPI
A digital photo is a grid of pixels. A printer places dots of ink on paper. DPI (dots per inch, and strictly PPI, pixels per inch, for images) tells you how many pixels are squeezed into one inch of paper. More pixels per inch means finer detail. The rule is simple:
print size (inches) = pixels ÷ DPI
For example, a 3000-pixel-wide image printed at 300 DPI is 10 inches wide. The same image at 150 DPI would be 20 inches wide, but each pixel is bigger and the picture looks less sharp when viewed up close.
Pixels needed for common print sizes (at 300 DPI)
| Print size | Pixels needed | Megapixels |
|---|---|---|
| 4 × 6 in (10 × 15 cm) | 1200 × 1800 | 2.2 |
| 5 × 7 in | 1500 × 2100 | 3.2 |
| 8 × 10 in | 2400 × 3000 | 7.2 |
| A4 (8.27 × 11.69 in) | 2481 × 3508 | 8.7 |
| A3 (11.69 × 16.54 in) | 3508 × 4961 | 17.4 |
| 11 × 14 in | 3300 × 4200 | 13.9 |
What can your photo do?
A phone photo of 4000×3000 pixels (12 megapixels) gives:
- at 300 DPI: 13.3 × 10 inches
- at 200 DPI: 20 × 15 inches
- at 150 DPI: 26.7 × 20 inches
So a 12-megapixel photo is more than enough for A4 and 8×10 prints. Posters can use lower DPI because people stand further from them.
Does changing DPI improve quality?
No. DPI is a number stored in the file’s header that suggests a print size. The pixel dimensions are what contain the detail. A 1000×1000 image labelled 300 DPI and the same image labelled 72 DPI are identical pixel for pixel. Printing software uses the label only to decide a default size, and you can override it. This also means “72 DPI for web” is a myth: on screens, only pixel dimensions matter.
Why enlarging does not help
If your photo is too small for the print size you want, scaling it up creates new pixels by guessing from their neighbours. The result is a bigger but softer picture. It does not gain detail. Better options are to print smaller, choose a lower-DPI large format that is viewed from further away, or retake the photo with a higher resolution. The Image Resizer is meant for shrinking and exact sizing; use enlargement sparingly.
Print aspect ratios and cropping
Camera photos are typically 3:2 or 4:3, while an 8×10 print is 4:5. Printing will crop or pad the photo unless you decide yourself. Crop first with the Image Cropper so you choose what is cut. See aspect ratios explained.
File format and compression for print
For print, keep a high-quality file: JPG at quality 90 or above, or PNG. Avoid heavy compression, and do not re-save repeatedly. For web use you can shrink freely; for print, keep the master. For the effect of compression levels, see our measurements.
Checklist
- Find your photo’s pixel dimensions (the resizer shows them).
- Divide by 300 to get the sharp print size in inches.
- Divide by 150 to get the maximum size for distant viewing.
- Crop to the paper’s ratio and send the original-size file to the printer.
Try it: Image Resizer
Resize to exact pixels or to a social media preset. Free, private, and it runs in your browser.
Open Image ResizerFrequently asked questions
What DPI should I use for printing photos?
300 DPI is the usual target for photos viewed close up. Large posters viewed from a distance can use 150 DPI or less.
Is 72 DPI for the web?
No. Screens use pixel dimensions only. The DPI label has no effect on how an image looks on screen.
Can I increase DPI to make a photo sharper?
No. Changing DPI only changes the suggested print size. The pixels stay the same.
How many megapixels do I need for an 8×10 print?
About 7.2 megapixels at 300 DPI (2400×3000 pixels).
Is my phone photo good enough to print?
A 12-megapixel photo is enough for prints up to about A4 at 300 DPI.