DPI vs PPI: What’s the Difference?

People often use DPI and PPI as if they were the same word. They are related, but they describe different things.

PPI: displays

PPI means pixels per inch. It describes how densely pixels are packed on a screen. The formula uses the diagonal:

PPI = Diagonal pixels / Diagonal inches, where diagonal pixels = sqrt(width² + height²).

A 1920 × 1080 screen at 24 inches diagonal is about 92 PPI. The same resolution on a 27-inch screen is about 82 PPI, because the same pixels are spread over a larger area.

DPI: printing

DPI means dots per inch, and it belongs to printing. A printer places dots of ink; a 300 DPI print places 300 dots per inch. For an image, effective print DPI is pixels divided by print inches.

Why the confusion?

Image software historically labelled a file’s intended print density as “DPI”, and some display settings also borrowed the term. In casual conversation the words are interchangeable, but for accurate work keep them separate: PPI for screens, DPI for print.

Try it: PPI Calculator · PPI vs DPI · DPI Calculator