What effective DPI means
DPI (dots per inch) is how many pixels of your image land on each printed inch. The same file can be 300 DPI at manga size and only 180 DPI blown up to magazine size, so a resolution only means something relative to a printed size. This checker scales your image to cover the full bleed box of the chosen format, exactly the way a printer's imposition will, and reports the resulting density.
Cover fit means one axis fits exactly and the other overhangs and gets cropped. The fitting axis sets the DPI. A page that is proportionally taller than the paper is limited by its width; a page that is proportionally wider is limited by its height.
Worked example
A standard US comic is 6.625 x 10.25 in. With 0.125 in bleed on every side the art area is 6.875 x 10.5 in. At 300 DPI that needs 2063 x 3150 pixels. A page exported at 1988 x 3075 (trim size, no bleed) is proportionally taller than the bleed box, so it is limited by width: 1988 / 6.875 = 289 DPI, and the checker calls it borderline. Add the bleed band instead of scaling up and it passes.
Thresholds
- 295 DPI and above: print ready. Rounding during export shaves a pixel or two, so 298 is not a failure.
- 200 to 294 DPI: borderline. Painted colour may pass; line art and small lettering go soft.
- Below 200 DPI: too low. Upscaling does not add detail; re-export from the source.
- If you set a resolution above 300 DPI (600 for line art, say), a page that clears 300 but falls short of yours is marked as under your target, not as a failure.
Read more in What DPI should a comic be? and check every page at once with the image validator.
Questions
What DPI should a comic page be?
300 DPI at the final printed size, including bleed, is the standard for colour and line art. Many artists work at 600 DPI for black-and-white line work.
Does the checker upload my image?
No. The image is decoded in your browser to read its pixel size and never leaves your device.
Why is my 300 DPI file reported as lower?
The file metadata says 300, but the pixel count is what matters. If the page was exported at trim size without bleed, filling the bleed box scales it up and lowers the effective DPI.