Change image DPI, 300 dpi without touching a pixel.

To change image DPI is to change one number stored in the file, the number of pixels per inch a printer should use. It does not change a single pixel. A 1600 x 1200 picture stays 1600 x 1200; only its printed size changes, because the printed size is the pixels divided by the DPI. This tool sets that number to 72, 150, 300 or any value from 1 to 10000 in JPG and PNG files, shows the printed size in inches and centimetres, and can also resample a picture to a paper size when you need more or fewer pixels.

How to set 300 dpi

1. Drop one or more JPG or PNG files on the box, or paste one with Command V or Ctrl V.
2. Under DPI, press 300, or type your own number in Or type your own.
3. Read the big printed size at the top. The table under it shows the same picture at 72, 96, 150, 300 and 600 dpi.
4. Leave Keep the pixels on to change only the number. Press Resample if you need a set print size and the pixels to go with it.
5. Press Download the picture, or Download all as ZIP for many files. The message under the picture says how many bytes changed.

The arithmetic of print size

Printed size in inches is pixels divided by DPI. A phone photo of 4000 x 3000 pixels at 300 dpi prints 13.33 x 10 inches, which is 33.87 x 25.4 cm, because one inch is 2.54 cm. The same file at 72 dpi would claim 55.56 x 41.67 inches. The picture is identical; only the label differs.

This is why a lower DPI number does not make a picture worse and a higher one does not make it sharper. If a print shop asks for 300 dpi at 8 x 10 inches, check the pixels, not the label: you need 2400 x 3000. A 1600 x 1200 picture set to 300 dpi prints only 5.33 x 4 inches at that density. To fill the sheet you must enlarge it, which Resample does, but no tool can add detail that was never captured.

Keep the pixels or resample

Keep the pixels is a header edit. For a JPG the tool rewrites the density in the JFIF header, which holds units, a horizontal density and a vertical density. If the JPG has no JFIF header, one is added at the front. It also updates the EXIF resolution tags and a Photoshop resolution note when they are present, so no program reads the old value. For a PNG it writes the pHYs chunk, which stores pixels per metre: 300 dpi is 300 divided by 0.0254, or 11811 pixels per metre. Everything else, including the compressed picture and the colour profile, is left as it was.

Resample draws the picture again at the size you pick. The tool turns the sheet to match the picture and either fills it, cropping the edges a little, or keeps the whole picture. At 8 x 10 inches and 300 dpi the result is 2400 x 3000 pixels. The colour profile is kept, and the DPI is written the same way. A big picture is halved in steps before the last step, which keeps small detail cleaner than one big jump.

The format specifications are public: the PNG specification defines the pHYs chunk and the JFIF specification defines the JPG density fields (read 18 Oct 2026).

Common problems

• The print shop still says 72 dpi. Some programs read a different field. This tool changes JFIF, EXIF and Photoshop notes, so it should match. Check the pixels as well: DPI alone does not make a file big enough.
• The file looks the same on screen. It should. A screen shows pixels and ignores the DPI.
• The file size is the same. Also expected. Keep the pixels adds a few bytes at most.
• It does not take my HEIC or WebP file. Those formats do not store a DPI the way JPG and PNG do. Convert to JPG first with the image converter.
• You can check the result on a Mac by opening the file in Preview and choosing Tools, then Adjust Size, or in Terminal with sips -g dpiWidth file.jpg.

For a screen's own pixel density rather than a file's, use the PPI calculator. To make the file smaller in bytes, use the image compressor, and to change the pixel size alone, the image resizer.