DPI checker
Read in your browser · the file is never uploaded
Reads the DPI an image declares and works out how large it will print at that density — and at any other you pick. Most files declare nothing at all, in which case software assumes 72.
How to use the dpi checker
The answer for most files is "none". Cameras, phones and screenshots frequently write no density at all, and software then falls back to 72 DPI — a number inherited from early Macintosh screens and meaningless for print. A file reporting 72 DPI usually has not been set rather than deliberately marked as low resolution.
What actually determines print quality is pixels against final size, which is why the print-size row matters more than the DPI row. The useful thresholds: 300 DPI is the standard for anything held in the hand — photographs, magazines, business cards. 150 DPI is fine for a poster viewed from a metre away. 72 to 100 is acceptable for a banner seen across a room, because the viewing distance does the work.
There is a real diminishing return above 300. The eye at normal reading distance resolves roughly 300 dots per inch, so 600 DPI on a photograph is a bigger file for no visible gain. Line art and text are different — those benefit up to 1200 because a hard edge shows stair-stepping the eye can see far past where it can resolve detail.
If a printer has rejected a file as low resolution, the fix is almost never changing the DPI field. It is either a larger original, or accepting a smaller print. Upscaling in an editor invents pixels and looks soft under the same scrutiny that flagged it.
Questions
Usually it means no density was set at all and software defaulted to 72. What matters is pixels against final print size.
Multiply the print size in inches by 300 for anything held in the hand. A 6 × 4 print needs 1800 × 1200.
For photographs, rarely — the eye resolves about 300 at reading distance. For line art and text, up to 1200 helps.
Get a larger original or print smaller. Changing the DPI field does not add detail, and upscaling invents it.
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