UsefulTab
DPI & Print Size Calculator
Pixels to print size, and rewrite DPI headers.
Calculate print size and set image DPI, locally
The calculator converts between pixel dimensions and physical print size at any resolution — enter width and height in pixels and a DPI (300 is the print standard) to see the size in inches and centimetres, or work backwards from a physical size to the pixels you need. The resampler then drops in a JPG or PNG and rewrites only its DPI metadata header, leaving every pixel byte untouched, so a print shop reads the right size without any quality loss from re-encoding. Everything runs in your browser — your files are never uploaded.
Common questions
What is DPI and why does 300 matter?
DPI (dots per inch) is how many pixels print into one inch of paper. It does not change the image's pixels — it tells a printer how large to render them. 300 DPI is the standard for sharp photo prints; 150 is acceptable for larger posters viewed from a distance, and 72 is a legacy screen value.
Does changing DPI resize or lower the quality of my image?
No. The resampler rewrites only the DPI metadata header (the JFIF density for JPG, the pHYs chunk for PNG). The image's pixel data is copied byte for byte, so there is zero re-encoding and no quality loss — only the stated print size changes.
How do I work out the pixels I need for a print?
Enter the physical size you want and the DPI, and the calculator shows the pixel dimensions required. For example, a 4×6 inch print at 300 DPI needs 1200×1800 pixels. If your image has fewer pixels than that, printing it that size will look soft.
Why does my file not show a current DPI?
Many images carry no DPI metadata at all, or only an aspect-ratio marker, in which case the resolution is undefined (software assumes 72 or 96). Setting a DPI with the resampler adds the proper header so it is explicit from then on.
Which file types can I resample?
JPG/JPEG and PNG. These are the formats that carry a standard, editable DPI header. Other formats would need re-encoding to change, which this tool deliberately avoids.
Is my image uploaded anywhere?
No. The file is read into memory in your browser, its header bytes are rewritten locally, and the result is offered as a download. Nothing is sent to a server.