"72 DPI for web, 300 DPI for print" is one of the most repeated rules in design — and one of the least accurate today. Here's where it came from and what actually still applies.
The original Macintosh display, in 1984, had a pixel density of almost exactly 72 pixels per inch — and Apple's software conveniently mapped that to 72 points per inch, a printing measurement, so a document would show on screen at roughly the size it would print. That coincidence is the entire origin of "72 DPI = screen resolution." It described one specific monitor, four decades ago.
Screens today have no fixed density. A phone screen can pack over 400 pixels per inch; a desktop monitor might sit anywhere from 90 to 220+. None of them are 72. The number never updated because it never needed to — screens don't read an image's DPI metadata at all. A browser or OS displays an image at one screen pixel per image pixel (before any CSS scaling), regardless of what density value is written into the file. For anything shown on a screen, the DPI field is simply inert.
300 DPI isn't arbitrary the way 72 is. It's close to the practical limit of what the human eye can resolve at a normal photo-viewing distance (roughly 12 inches), and it lines up well with what offset and photographic printing processes can reproduce without visible dot patterns. That combination made 300 DPI the de facto standard for photo labs, magazines, and most professional print workflows — and it has held up because the physics behind it hasn't changed.
If it's only ever going to be viewed on a screen, its DPI metadata doesn't matter — set it to whatever, or leave it alone. If it's going to print, 300 DPI is the safe, standard target for photos and documents viewed up close; large posters and banners viewed from a distance can often use 150–200 DPI or less without any visible loss of sharpness, since the viewer is further away.
Changing DPI updates print metadata. It does not create new pixels. Whatever target you pick, setting it is only half the job — the image also needs enough actual pixels to support that density at your print size. Use the 300 DPI Converter to set the metadata, and the DPI Checker to confirm what an image already has before you send it anywhere.
