Change image DPI (72 to 300 DPI)
Set a JPG or PNG to 300 DPI without re-encoding a single pixel, or resample it to an exact print size. Reads and writes JFIF, EXIF and pHYs tags.
- Runs in your browser
- Files are never uploaded
- Free, no account
What DPI actually is
DPI (dots per inch, sometimes PPI) is a label, not a property of the image data. It tells whatever lays the image out on paper how big one pixel should be. A 600 × 600 pixel image tagged 300 DPI prints at 2 × 2 inches; the identical file tagged 72 DPI prints at 8.3 inches and looks blurry — even though not a single pixel changed. Nothing about the sharpness of the file changes when you change the tag; only the intended physical size does.
That is why setting DPI here is instant and completely lossless: we patch the density field in the file header and leave the compressed image data untouched, byte for byte.
So why do forms demand 300 DPI?
Two reasons. First, layout software reads the tag to place the image, and a file with no tag defaults to 72 DPI — which lays it out more than four times too large, so the reviewer sees a soft, oversized picture. Second, “300 DPI” is a shorthand that submission guidelines use to mean “enough pixels to print well”, even though the tag alone cannot deliver that. Set the tag to satisfy the checker, and check the pixel count to satisfy the printer.
Where the number is stored
| Format | Field | Units | Can we write it? |
|---|---|---|---|
| JPEG | JFIF APP0 segment: units, Xdensity, Ydensity | Per inch or per cm | Yes — patched in place, or inserted if absent |
| JPEG with EXIF | IFD0 tags XResolution (0x011A), YResolution (0x011B), ResolutionUnit (0x0128) | Rational, inch or cm | Yes — updated so it cannot disagree with JFIF |
| PNG | pHYs chunk | Pixels per metre | Yes — rewritten or inserted after IHDR, with a fresh CRC32 |
| WebP, GIF, BMP | No standard density field | — | No — convert to JPG or PNG first |
The dual JPEG write matters in practice: some applications read JFIF, others prefer EXIF, and a file where the two disagree lays out differently depending on who opens it. This tool keeps them in step.
Set DPI only, or resample?
- Set DPI only — the header is rewritten and nothing else. Use this when the pixel count is already right and a form or a designer just needs the tag to say 300. It is instantaneous and cannot degrade the image, because the image data is not touched.
- Resample — you specify the physical size and the DPI, and the tool computes the pixel dimensions and resizes to them with a Lanczos3 filter, then writes the tag. Use this when the printed size must be exact. It re-encodes, so it is not lossless, and it warns you when the target would require upscaling.
The arithmetic, both ways
Pixels = inches × DPI, and inches = pixels ÷ DPI. So a 4 × 6 inch print at 300 DPI needs 1200 × 1800 pixels, and a 3000 × 2000 pixel photo tagged 300 DPI prints at 10 × 6.67 inches. The table on the page does this for your specific image at every common resolution, in both inches and centimetres, so you can see at a glance whether your file is big enough for the print you have in mind.
Choosing a resolution
| DPI | Use |
|---|---|
| 72 / 96 | Historic screen defaults. Still the fallback when a file has no tag at all. |
| 150 | Draft printing, newspapers, large posters seen from a distance. |
| 200 | Everyday office laser output; often the practical limit of the paper. |
| 300 | The standard for photo prints, passport photos, magazines and most submission guidelines. |
| 600 | Line art, engravings, fine text, high-quality scans. |
| 1200 | Archival scanning and reprographics. Enormous files; rarely necessary for photographs. |
Common misconceptions
- “Changing DPI to 300 will make my photo higher quality.” No — it makes the printed version smaller, which can look sharper on paper, but adds no detail.
- “My 72 DPI image is low resolution.” The tag says nothing about resolution. A 6000 × 4000 photo tagged 72 DPI has exactly as much detail as the same file tagged 300.
- “DPI affects how it looks on screen.” Browsers and most viewers ignore it entirely; they lay images out in pixels. It matters at print time and in page-layout software.
- “Resampling up to 300 DPI fixes a small image.” It only invents pixels by interpolation. The tool tells you when that is what you are asking for.
Related tools
Passport Photo Maker writes 300 DPI automatically for document photos, Resize Image changes pixel dimensions directly, and Image Metadata Viewer shows the full EXIF block including the resolution tags this tool writes.
Questions
Does changing DPI improve image quality?
No. DPI is a label saying how large one pixel should be on paper; it changes nothing about the pixels themselves. A 600 × 600 image tagged 300 DPI prints at 2 × 2 inches; the same file tagged 72 DPI prints at 8.3 inches and looks blurry. The pixels are identical in both cases.
So why do submission forms ask for 300 DPI?
Because their layout software reads the tag to decide the physical size, and because a file with no tag defaults to 72 DPI, which lays out four times too large. Setting the tag is the entire fix — and it is lossless.
Where is the DPI actually stored?
In JPEG it lives in the JFIF APP0 segment (units plus X and Y density), and often duplicated in the EXIF XResolution tags. In PNG it is the optional pHYs chunk, in pixels per metre. We patch all of them so no two readers disagree, and we add the segment or chunk when the file has none.
What is the resample mode for?
For when the physical size must be exact and the pixel count has to change to match — “I need this at 4 × 6 inches at 300 DPI” becomes a 1200 × 1800 pixel image. That mode does re-encode, using a Lanczos3 filter, and warns you when it would have to upscale.
Why can I not set the DPI of a WebP or GIF?
Those containers have no standard density field, so there is nothing to write. Convert to JPG or PNG first, then set the DPI.