Change image DPI
Open a JPG or PNG and choose 300 DPI or any value from 1 to 65,535. If you change nothing else, only the header is rewritten: the pixels are not re-encoded, and the file grows by 21 bytes at most. The DPI sets the print size, so 3000 pixels print 10 inches wide at 300.
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Open a photo to see how large it prints.
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What does changing the DPI change?
Only the print size. A digital photo is a grid of pixels, and its DPI is a number in the file's header saying how many of them to fit into each inch of paper. Screens ignore it.
So one 3000 x 2000 photo prints at four different sizes, with every pixel identical:
| DPI in the file | Print size | In centimetres |
|---|---|---|
| 72 DPI | 41.67 x 27.78 in | 105.8 x 70.6 cm |
| 150 DPI | 20 x 13.33 in | 50.8 x 33.9 cm |
| 300 DPI | 10 x 6.67 in | 25.4 x 16.9 cm |
| 600 DPI | 5 x 3.33 in | 12.7 x 8.5 cm |
A higher DPI makes the print smaller and denser. It never adds detail, because no pixel is added.
Why printers, scanners and screens each mean something different by DPI: What DPI means, and what it does not change.
How many pixels do you need to print at 300 DPI?
Multiply each side in inches by the DPI. If a print shop or a form asks for 300 DPI, these are the pixel counts to reach:
| At 300 DPI | At 150 DPI | |
|---|---|---|
| 4 x 6 in photo | 1200 x 1800 | 600 x 900 |
| 5 x 7 in photo | 1500 x 2100 | 750 x 1050 |
| 8 x 10 in photo | 2400 x 3000 | 1200 x 1500 |
| A4 page (210 x 297 mm) | 2480 x 3508 | 1240 x 1754 |
| Passport photo (35 x 45 mm) | 413 x 531 | 207 x 266 |
With fewer pixels than the row you need, a higher DPI shrinks the print instead. Setting 300 DPI on a 1200 x 800 photo prints it at 4 x 2.67 inches, not 6 x 4.
The panel above reads this out as you change the DPI, in inches and centimetres, for the photo you opened.
These print sizes have a page that opens at them, with the DPI already set:
- Resize an image to 35 x 45 mm
- Resize an image to 4 x 6 inches
- Resize an image to 5 x 7 inches
- Resize an image to 8 x 10 inches
- Resize an image to A4 size
More print sizes, and the far lower DPI print labs say they accept: Photo print sizes in pixels, and what labs really need.
Why does my computer still show the old DPI?
Because a JPEG can store its DPI twice: once in the JFIF header, and again in the EXIF block that cameras and photo editors write. They are separate bytes, and nothing forces them to agree.
We tested what happens when they differ. On a camera JPEG declaring 240 DPI in both, we changed only the JFIF value to 300. The macOS sips tool still reported 240, while Python's Pillow library reported 300.
PNG has the same split. Its DPI lives in a pHYs chunk, and a PNG can carry EXIF as well. Changing only the pHYs chunk on a test PNG left macOS reporting 72.
This tool rewrites every copy it finds, so they all say the same number. When you open a photo, the panel shows what it declares, including when it declares two different values.
When should you add pixels instead?
When the print has to stay the same size at a higher DPI. That needs more pixels, and enlarging a photo invents them by blending neighbours, so the print gets bigger and softer rather than sharper.
To resample here, switch the size fields from px to cm, mm or in, then choose the DPI you need. The print size stays as it is and the pixels change to match.
Or stay in px and type a new width: the print size updates as you type. Either way the download is re-encoded with the DPI written in.
Better still, start from the largest original you have rather than a copy that was already shrunk.
Which formats can keep a DPI?
JPEG and PNG. JPEG keeps it in the JFIF header and often in EXIF too, and PNG keeps it in a pHYs chunk. This tool writes all of them.
WebP and AVIF have no DPI field of their own. They can only carry one inside EXIF metadata, which this tool does not write, so a WebP or AVIF download here has no DPI.
HEIC, GIF and BMP open here too. Saving one as JPEG or PNG gives it a DPI, but that is a conversion, so the image is re-encoded.
What happens to your photo?
Your selected photo is processed in your browser, without an image upload to a server. The page may download code and codecs needed for editing.
Save your result before closing the tab; unsaved edits are kept in memory rather than in an online account.
Common questions
Does changing the DPI reduce quality?
Not here, when the DPI is all you change. The download is your original file with a new header, so every pixel stays exactly as it was. Resizing, cropping, turning or converting re-encodes the image, and the panel says when that happens.
Does changing the DPI change the file size?
Barely. Rewriting a DPI the file already has adds nothing. Adding one to a file that had none adds 18 bytes to a JPEG or 21 to a PNG. The pixel count, which is what drives file size, stays the same.
Can I set the size in centimetres or inches?
Yes. Switch the size fields from px to cm, mm or in, and type the print size you want. The tool works out the pixels at your DPI and shows them under the fields, so 3.5 cm at 300 DPI reads 413 pixels.
How do I check an image's DPI?
Open it in the tool above. The panel reads the file's own headers and says what DPI it declares, or that it declares none. On a Mac, Preview's inspector shows it too, and on Windows the file's Properties, under Details.
Does 72 DPI mean my photo is low quality?
No. 72 is only a number in the header, often a program's default. A 4000 x 3000 photo marked 72 DPI has exactly the pixels it would have marked 300. It would print 55.56 inches wide instead of 13.33.
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