Three calculators built around one formula: pixels divided by DPI equals inches. Everything else on this site explains that number from a different angle.
PrintDPI started as a single question someone kept typing into a search bar: will this photo look sharp at this size? The math behind that question is not complicated, but it is easy to get backward, so the site turned into three calculators plus the background needed to use them without guessing.
The Print Size Calculator takes the pixel dimensions of an image and a target DPI, and returns the largest size you can print without it turning soft. The Required Resolution Calculator runs the same equation backward: tell it the print size and DPI you want, and it tells you the pixel count the file needs. The DPI Calculator checks an existing pairing of pixels and print size and reports the actual DPI you would get. All three run in the browser the moment you stop typing, and none of them upload an image anywhere.
Most sites explaining DPI walk through paragraphs of theory before getting to a usable answer. PrintDPI flips that: the calculator comes first, the explanation is optional. The DPI and print resolution guide and the shorter articles under Articles exist for anyone who wants the reasoning, not because the number needs it.
Chris Terry owns and maintains PrintDPI as part of the Encore Editorial group of sites. The guides and reference pages are written by Marcus Vance, whose full background is on the authors page. Chris reviews what publishes here but does not write the articles himself. The approach both of them follow, how a figure gets checked and how a correction gets handled, is laid out on the editorial standards page.