DPI converter and checker
Read in your browser · the file is never uploaded
Reads the DPI an image declares, works out how large it prints at that density and at any other you pick, then writes a new value without re-encoding anything. Most files declare nothing at all and software falls back to 72. A 6 × 4 inch print at 300 DPI needs 1800 × 1200 pixels, whatever the field says.
How to use the dpi converter and checker
DPI is metadata, not resolution, and that is the one thing worth taking away. An image is a grid of pixels; the DPI is a note attached to it saying how large to print that grid. A 3000-pixel-wide photo is 10 inches at 300 DPI and 30 inches at 100 DPI. The same pixels either way. Changing the number changes the intended print size and nothing about the image.
For most files the declared answer 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 has usually not been set rather than deliberately marked as low resolution, which is why the print-size row matters more than the DPI row.
This is also why "make this 300 DPI" is an incomplete request. If a printer asks for 300 DPI they mean 300 pixels for every inch of the final printed size, so a 6 by 4 inch print needs 1800 by 1200 pixels. Setting the DPI field on a 600-pixel image to 300 does not create detail; it says "print this at 2 inches wide". The print size is shown at both the current and the new DPI for exactly that reason.
The useful thresholds: 300 DPI 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, since the eye at normal reading distance resolves roughly 300 dots per inch; line art and text are the exception and benefit up to 1200, because a hard edge shows stair-stepping long past where the eye can resolve detail.
The write is lossless because it edits a header rather than re-encoding. JPEG stores density in the JFIF APP0 segment; PNG stores it in a pHYs chunk, in pixels per metre rather than per inch. Both are a handful of bytes near the start of the file. Doing the same by opening and re-saving in an editor would recompress the entire image to change one number, which for a JPEG loses quality every time.
If a printer has rejected a file as low resolution, changing this field is almost never the fix. The answer is a larger original, or a smaller print. Upscaling in an editor invents pixels and looks soft under the same scrutiny that flagged it in the first place.
Where the field is ignored entirely: screens. A browser, a phone and a monitor all disregard DPI completely and show the pixels. It only affects print and page-layout software.
What people use it for
- Checking whether a photo is really 300 DPI before sending it to a printer
- Finding out how large a file will print at the density it declares
- Working out the pixel count a 6 × 4 inch print actually needs
- Setting a scan to 300 DPI for a print shop that insists on the field
- Changing a declared density without re-compressing a JPEG
Questions
Usually it means no density was set at all and software defaulted to 72. What matters is pixels against final print size.
No. It changes a note about intended print size. The pixels are identical, and no detail is created.
300 pixels for every inch of the final print. A 6 × 4 inch print needs 1800 × 1200 pixels, whatever the DPI field says.
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.
Yes. It rewrites a header field. Re-saving in an editor would recompress the whole image to change one number.
Get a larger original or print smaller. Changing the DPI field does not add detail, and upscaling invents it.
Barely. The density is a handful of bytes near the start of the file, and nothing else is rewritten.
For a file, yes — both name the same field. Strictly, PPI counts pixels in an image and DPI counts ink dots a printer lays down, and a printer uses several dots per pixel.
In a JFIF APP0 segment for JPEG and a pHYs chunk for PNG, which records pixels per metre. GIF has no density field at all, and WebP carries one only inside an embedded EXIF block.
Screens always do. Only print and page-layout software use the field.
No. Everything happens in your browser; you can load the page, go offline, and it still works.