PPI and DPI show up interchangeably in almost every image editor, print shop order form, and online tool — including, in places, this one. They're close enough in everyday use that the mix-up rarely causes real problems, but they technically describe two different things.
PPI stands for pixels per inch. It describes how densely an image's own pixel grid is packed into a physical inch once you decide on a print size. A 3000-pixel-wide image printed at 10 inches wide has 300 PPI; the same image printed at 20 inches wide has 150 PPI. PPI is really just pixel count divided by print size — it doesn't exist independently of both those numbers.
DPI stands for dots per inch, and strictly speaking, it describes how many individual dots of ink or toner a printer physically deposits per inch to reproduce a pixel — including dithering dots a printer uses to approximate colors and tones it can't print directly. A printer's DPI is a hardware specification; it's not something an image file inherently has.
Image files store a density metadata field — the one this site's tools read and edit — and that field is almost universally labeled "DPI" in software, even though what it actually encodes is closer to the PPI definition: a target pixel density for printing. That labeling convention is decades old at this point, and fighting it in casual conversation isn't worth the confusion it would cause. In practice, when someone says an image "needs to be 300 DPI," they mean its pixel dimensions need to support 300 PPI at the size it'll be printed.
Changing DPI updates print metadata. It does not create new pixels. Whichever term you use, the only thing that determines how sharp a print can look is whether the image has enough pixels for its intended print size — not what number is written into its metadata. Check yours with the DPI Checker, and if you need to hit a specific pixel target, the Print Size Calculator will tell you exactly what you need.
