What DPI is, and what it is not
DPI, dots per inch, is a number stored in an image file that tells a printer how large to make the picture on paper. It does not add pixels, change how sharp the picture is or alter its file size. A 1200 × 1800 pixel image is the same pile of pixels whether the file says 72 DPI or 300 DPI; what changes is the physical size at which a printer or layout program will output it by default. At 300 DPI it prints at 4 × 6 inches; at 72 DPI the same pixels would print at about 16.7 × 25 inches, and look coarse.
| Pixels | At 72 DPI | At 150 DPI | At 300 DPI |
|---|---|---|---|
| 1200 × 1800 | 16.7 × 25 in | 8 × 12 in | 4 × 6 in |
| 2400 × 3000 | 33.3 × 41.7 in | 16 × 20 in | 8 × 10 in |
| 600 × 600 | 8.3 × 8.3 in | 4 × 4 in | 2 × 2 in |
Why a form asks for 300 DPI
Many application forms and print services ask for a photo or a scan at 300 DPI. Often, all that is checked is the number stored in the file, so a picture that is perfectly fine can be refused simply because it says 72. In that case you do not need to resample or enlarge anything: changing the stored value is enough, and the pixels stay as they are. This page does exactly that, for JPG and PNG, leaving the image data and the quality untouched.
How to change it
- Drop your image on this page and choose the DPI you need: 300 is the usual one, and 72, 150 and 600 are available too.
- The tool shows the print size that results, so you can see whether it is what you expect.
- Download the file. The pixels and the quality are exactly the same as before.
When DPI is not enough
If you need a larger print, the number of pixels is what matters. To print 8 × 10 inches at 300 DPI you need 2400 × 3000 pixels. A smaller image labelled 300 DPI does not become sharper; it just claims a smaller print. If a form asks for both a resolution and pixel dimensions, set them together by switching on the dimensions requirement as well, and use the table above to check they agree. WebP does not have a field for DPI, so choose JPG or PNG when resolution is part of the requirement.
The guide on pixels, DPI and resolution explains how these ideas fit together, and it is a good place to start if print sizes are new to you. For passport photos, which have their own pixel rules, see passport photo size in pixels.