Image DPI Changer with Print Size (mm) Preview
Rewrite only the DPI metadata stored in a PNG (pHYs chunk) or JPEG (JFIF header). The pixel data is never touched, so there is no quality loss and the pixel dimensions stay the same. You also get the print size in mm at the new DPI and whether the image fits A4, B5 and other paper sizes. To change the pixel dimensions themselves, use the Image Resizer; for paper size and pixel math, see the Print Size Converter.
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PNG and JPEG are supported. You can also drag and drop a file here
A whole number from 1 to 65535. 300 dpi is typical for print and 72-96 dpi for screens.
Print size
Paper fit
The image orientation is matched automatically. "Min. DPI" is the lowest DPI at which the image does not overflow the paper.
| Paper | Size (mm) | Min. DPI | At this DPI |
|---|
How to use
- Pick a PNG or JPEG with "Choose an image file" (drag and drop also works)
- The current DPI, pixel size and print size in mm are shown
- Enter a value in "New DPI" or pick a preset; the print size and paper fit update
- Click "Rewrite DPI and download" to save the file
Notes
- Only the metadata is rewritten; the pixel data is not re-encoded. Pixel size, quality and colors stay as they were, and the image is not scaled when you change the DPI.
- DPI only says how many pixels per inch to use when printing. Raising it on a low-resolution image does not add detail.
- If a JPEG has no JFIF header (for example a photo with only Exif), a JFIF APP0 segment is added at the start to store the DPI. The resolution tags inside Exif are left unchanged, so some software may still show the old Exif value.
- Formats other than PNG and JPEG (GIF, WebP, BMP and so on) cannot be rewritten. Use the image format converter if you need to change the format.
- Some apps and print software ignore the embedded DPI and decide the size from the pixel count alone.
Glossary
DPI
Dots per inch (25.4 mm). The DPI stored in an image is a hint for the default print or layout size; it does not change the pixel count.
pHYs (PNG)
The PNG chunk that stores the physical pixel dimensions. It is saved as pixels per meter, so 300 dpi becomes 11811 pixels/meter (about 299.9994 dpi).
JFIF (JPEG)
The APP0 segment at the start of a JPEG. It holds the density unit (dpi, dpcm or aspect ratio only) and the horizontal and vertical density as two bytes each.
FAQ
Does changing the DPI affect image quality?
No. Only metadata (the PNG pHYs chunk or the JPEG JFIF header) is rewritten and the pixel data is not re-encoded, so the pixel size and quality stay exactly the same.
Will setting 300 DPI make my print sharper?
No. DPI only sets the intended print size; sharpness depends on the pixel count. To print A4 at 300 dpi you need about 2480 x 3508 px or more. Check the "Min. DPI" column in the paper fit table to see what your image supports.
Another app still shows a different DPI after I changed it. Why?
If a JPEG keeps resolution tags in its Exif data, some software reads those instead of the JFIF header. Other apps ignore the embedded DPI entirely and work from the pixel count.
Can I change the DPI of a GIF or WebP file?
No. This tool rewrites PNG and JPEG only, and shows an error for other formats. Convert the file to PNG or JPEG with the image format converter first.
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