"Submit your photo at 300 DPI." It's a common instruction on exam and print forms, and it confuses a lot of people. Here's what DPI really means, how it differs from pixels, and how to set it in seconds.
What DPI actually means
DPI stands for dots per inch — the print resolution stored in an image file. It tells a printer how many pixels to pack into each inch of paper, which decides how large (and how sharp) the photo prints. 300 DPI is the standard for crisp printing and is what most exam and passport forms expect.
DPI vs pixels — the key difference
This trips everyone up: DPI doesn't change the number of pixels in your image. A 600×600 px photo is still 600×600 px whether it's tagged 72 DPI or 300 DPI — what changes is the print size. At 300 DPI those 600 pixels print as 2 inches; at 72 DPI they'd print much larger and look blocky. So DPI is about printing, not the pixel dimensions on screen.
How to change a photo's DPI
Use Change Image DPI: pick 300 (or any value), upload your photo, and download. The tool writes the DPI into the file without resampling the pixels, so the image stays the same size and just reports the correct DPI. It runs in your browser, so nothing is uploaded.
Getting both DPI and physical size right
Some forms want a specific physical size and 300 DPI — for example a 3.5×4.5 cm photo at 300 DPI. Set the size first with resize in cm (it works out the pixels for you), or the Image Resizer for pixels, then set the DPI. Always confirm the exact requirement in your official instructions.