DPI converter: change the DPI of an image
Choose a PNG or JPEG, set the DPI you need, and download it. Only the resolution stored in the file changes: the pixels are not re-saved, so no quality is lost.
Free, no account. The file is read by code running in your browser. It is not uploaded, and nothing about it is stored.
How to change an image to 300 DPI
- Choose your PNG or JPEG.
- Type the DPI you need, or tap 300.
- Check the print size shown for that DPI.
- Download. The file has the same pixels and the new DPI.
What changing the DPI does, and does not do
The DPI in an image file is a short note that says how many of its pixels to print in each inch. It decides how large the picture prints; it does not change how many pixels there are or how sharp they are. A 3000 × 2400 pixel photo marked 72 DPI and the same photo marked 300 DPI are identical on a screen. On paper the first is 41.7 × 33.3 inches and the second 10 × 8.
This tool rewrites that note and nothing else. In a PNG it is the pHYs chunk; in a JPEG it is the JFIF header or the EXIF resolution fields. The compressed picture data is copied across byte for byte, which is why a JPEG can be changed here with no loss at all. Photo editors usually re-compress a JPEG when they save it.
When 300 DPI will not make it sharper
If a form or a printer demands “300 DPI”, they nearly always mean enough pixels for the print size at 300 pixels per inch. Setting the DPI satisfies an upload check, but only pixels make a sharp print. The tool shows the size your picture prints at the DPI you choose. If that is smaller than you need, the picture does not have enough pixels, and no DPI setting can add them.
Work out what you need on the DPI calculator: 8 × 10 inches at 300 DPI takes 2400 × 3000 pixels.
A note on PNG and exact numbers
PNG stores resolution in pixels per metre, as a whole number. 300 DPI becomes 11,811 pixels per metre, which is 299.9994 DPI. Some programs show that as 299.999 and most round it to 300. It is the nearest a PNG can hold.
Questions
Does changing the DPI reduce quality?
No. Here the pixels are not decoded or saved again, so the picture is exactly the same. The file changes by a few bytes.
Does it change the file size or the pixel dimensions?
No. The width and height in pixels stay the same, and the file grows or shrinks by at most a few bytes.
Which files does it take?
PNG and JPEG. Other formats, such as WebP, TIFF and HEIC, are not supported yet.
How do I make a picture print larger at 300 DPI?
It needs more pixels, which means resampling it in a photo editor, and that cannot add real detail. Start from the largest original you have.