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What Image Size Do You Need for Printing?
How to work out whether your photo is big enough to print, what DPI actually means, and what to do when the file falls short.
The only sum you need
Pixels needed = print size in inches x 300
A 4 x 6 inch print needs about 1200 x 1800 pixels. An A4 page needs roughly 2480 x 3508 pixels.
That 300 figure is the standard for good quality photographic printing. It is not a law of physics, and you will see perfectly acceptable prints at lower numbers, but it is the target professionals work to.
What DPI really means
DPI stands for dots per inch: how many dots of ink the printer lays down in one inch of paper. A closely related term, PPI, means pixels per inch in the file itself. In everyday use people say DPI for both.
Here is the part that confuses almost everyone: the DPI number stored inside an image file does nothing on its own. A photo is a fixed grid of pixels. Changing the stored DPI value from 72 to 300 in an editor does not add a single pixel; it only changes the size the file suggests when printed. What matters is the pixel count and the physical size you want.
Common print sizes
| Print size | Pixels at 300 DPI | Acceptable minimum (200 DPI) |
|---|---|---|
| 4 x 6 in | 1200 x 1800 | 800 x 1200 |
| 5 x 7 in | 1500 x 2100 | 1000 x 1400 |
| 8 x 10 in | 2400 x 3000 | 1600 x 2000 |
| A4 | 2480 x 3508 | 1654 x 2339 |
| A3 | 3508 x 4961 | 2339 x 3307 |
Viewing distance changes everything
The 300 DPI rule assumes something held at arm's length. The further away a print will be viewed, the fewer pixels per inch you need, because your eye cannot resolve the difference.
- Photo prints and books: 300 DPI
- Posters viewed from a metre or two: 150 to 200 DPI is usually fine
- Large banners seen from several metres: 100 DPI or even less
This is why a billboard can be printed from a file that would look terrible as a postcard.
When your file is too small
Suppose you have a 900 x 600 photo and you want an 8 x 10 inch print, which calls for 2400 x 3000. You are short by a wide margin. There are three honest options.
Print smaller. At 900 x 600 you can make a good 3 x 2 inch print. Often the simplest answer.
Accept a lower DPI. Stretching 900 x 600 across 8 x 10 inches gives about 90 DPI, which will look soft up close but may be acceptable if the print will hang on a wall.
Upscale it first. An AI upscaler can take that 900 x 600 to 3600 x 2400, which comfortably exceeds what the 8 x 10 needs. This works far better than letting the printer stretch the file, because the model reconstructs edges and texture instead of simply averaging pixels.
Practical steps before printing
- Decide the physical size you want.
- Multiply each side by 300 to get the pixels you need.
- Check your file's actual pixel dimensions (right-click, Properties or Get Info).
- If you are short, upscale the image to at least the required size.
- Save as PNG for maximum quality, or JPG at highest quality if the printer asks for it.
- Check the aspect ratio matches the paper, or expect cropping.
One warning about aspect ratio
A 4 x 6 print is a 2:3 shape. An 8 x 10 is 4:5. Most phone cameras shoot 4:3. These do not match, so something will be cut off. Crop deliberately before printing rather than letting the lab decide where to cut.