How to change the DPI of an image
Drop in a JPEG or PNG. The tool reads the resolution the file declares and shows where it came from — EXIF, JFIF or the PNG pHYs chunk — or tells you the file has no DPI set at all, which is common for screenshots and images exported from web tools. Pick 300 or type any value, check the print size it implies, and download. The new file has the same pixels and nearly the same byte size as the original; only the header number changes.
Because nothing is resampled, this is the right fix when a form rejects an image for having “72 DPI” even though it has plenty of pixels. If the print-size table shows the image would print too small at 300 DPI, the honest fix is a larger original — upscaling with the Image Resizer adds pixels but not detail.
DPI, PPI and pixels in one paragraph
A digital image has only pixel dimensions. DPI (strictly PPI, pixels per inch) is an instruction to the printer: spread those pixels at this density. Divide pixel width by DPI and you get print width in inches — 3000 pixels at 300 DPI is 10 inches. Screens ignore the value entirely, which is why changing it makes no visible difference on your monitor. Our guide to DPI vs PPI covers which values to use for photos, posters and documents.
Common DPI targets
300 DPI is the standard for photo prints, brochures and anything viewed at arm’s length. 150–200 DPI is acceptable for posters and large prints viewed from a distance. 600 DPI suits line art and scanned text. 72 and 96 DPI are legacy screen conventions with no effect on how an image looks online. If a portal also caps the file size, run the result through Compress Image to Size afterwards; it re-encodes the pixels, so set the DPI again last if the portal checks both.