What DPI actually changes
DPI (dots per inch, also written PPI) is a single number stored inside an image file. It does not change a single pixel; it tells a printer or a layout program such as Word, InDesign or Canva how many of those pixels to fit into each inch of paper. The same 1800×1200 photo prints at very different sizes depending on that number:
| DPI stored in the file | Print size of a 1800 × 1200 px photo | Typical use |
|---|---|---|
| 72 | 25 × 16.7 in (63.5 × 42.3 cm) | Old screen default; what most phone photos say |
| 96 | 18.75 × 12.5 in (47.6 × 31.8 cm) | What Windows assumes when no DPI is stored |
| 150 | 12 × 8 in (30.5 × 20.3 cm) | Posters and banners seen from a distance |
| 300 | 6 × 4 in (15.2 × 10.2 cm) | Photo prints, books, print shops, most forms that ask for “300 DPI” |
| 600 | 3 × 2 in (7.6 × 5.1 cm) | Line art and scans that must stay crisp when small |
That is why a print shop or a publisher asks for “300 DPI”: they want to know the picture will be printed at a size where it still looks sharp. If your photo has enough pixels, changing the stored number is all that is needed, and that is what this page does. Use Print size above to type the width you want on paper; the page works out the DPI from each image’s own pixel width.
Why Windows can still say 72 dpi after you changed it
A JPG can hold its resolution in up to four places: the JFIF header that nearly every JPG starts with, the EXIF data that phones and cameras add, a Photoshop resource block, and XMP metadata. A PNG keeps it in a chunk called pHYs. None of the online DPI converters we looked at mention that there is more than one.
We built test JPGs where the records disagree and opened them with three readers on Windows 11 (October 2026): the Python image library Pillow, and the two image readers built into Windows that File Explorer and many desktop programs use.
| What the file contains | Windows (File Explorer, GDI+, WIC) | Pillow (Python) |
|---|---|---|
| JFIF 300, no EXIF | 300 | 300 |
| No JFIF, EXIF 72 (straight from a phone) | 72 | 72 |
| JFIF 300 + EXIF 72 (phone photo after a JFIF-only change) | 72 | 300 |
| JFIF 72 + EXIF 300 (EXIF-only change) | 300 | 72 |
| JFIF 300 + EXIF 300 (this page) | 300 | 300 |
| JFIF with no unit, no EXIF | 96 | none |
| PNG with pHYs 300 | 300 | 300 |
| PNG without pHYs | 96 | none |
So when both records exist, Windows goes by EXIF and Pillow goes by JFIF. A phone photo changed by a tool that rewrites only the JFIF header still shows 72 dpi in File Explorer’s Details tab, and a print shop’s upload checker may see a different number from the one you checked. This page rewrites every record it finds, adds a JFIF header when the file has none, then reads the saved file again and lists each value so you can see they match.
No re-saving, no quality loss
Many editors change the DPI by opening the picture and saving it again, and saving a JPG again compresses it again. Here only the small header records are rewritten: the compressed image data, everything from the start-of-scan marker of a JPG or the IDAT chunks of a PNG, is copied byte for byte, and the page compares it with the original after saving. In our tests the saved files were 0 to 21 bytes larger than the originals: 21 is a PNG that had no DPI record yet. Camera settings, the date taken, GPS and the colour profile stay as they were; to remove those, use Remove EXIF data.
Does 300 DPI make my picture high resolution?
Only if it already has enough pixels for the size you need. A form or a print shop that asks for “300 DPI at 4 × 6 inches” really wants 1200 × 1800 pixels. Setting a 600 × 900 picture to 300 DPI makes it print at 2 × 3 inches; setting it to 150 DPI makes it print at 4 × 6 but softer. Neither adds detail. The result list shows the print size of every file at the DPI you chose, so you can see at a glance whether the picture is big enough.
| Print size | Pixels needed at 300 DPI |
|---|---|
| 2 × 2 in (passport photo) | 600 × 600 |
| 4 × 6 in | 1200 × 1800 |
| 5 × 7 in | 1500 × 2100 |
| 8 × 10 in | 2400 × 3000 |
| A4 (8.27 × 11.69 in) | 2480 × 3508 |
Other formats
This page changes JPG (including .jfif) and PNG. WebP and HEIC have no standard DPI record that printers read; convert them first with Convert image format or HEIC to JPG. For a TIFF at a set DPI, use JPG to TIFF or PNG to TIFF, which write the resolution you choose.
Related tools
To change the size in pixels rather than the print size, use Resize image. For a passport or visa photo printed at exactly 2 × 2 inches, the US passport photo maker lays out the print sheet for you. And if a form limits the file size as well as the DPI, finish with Compress image to an exact size, then change the DPI here again: the DPI survives this page, but not every compressor keeps it.