PPI Calculator
Work out a display's pixels per inch and dot pitch from its resolution and diagonal size.
How it works
PPI, pixels per inch, tells you how tightly packed a screen's pixels are — the higher the number, the sharper text and images look. It depends on both the resolution and the physical size, so a big 4K TV can have fewer PPI than a small phone.
The formula uses the Pythagorean theorem: take the pixel count across the diagonal, which is the square root of width squared plus height squared, then divide by the diagonal in inches. A 2560×1440 panel on a 27-inch screen works out to about 109 PPI.
Dot pitch is the flip side — the distance between pixel centres, usually in millimetres. It's just 25.4 (millimetres per inch) divided by the PPI, and smaller is sharper.
Frequently asked questions
What's a good PPI for a monitor?
Around 90 to 110 PPI is comfortable for a desktop monitor at normal viewing distance. Phones push far higher, often 300 to 500 PPI, because you hold them close to your face.
Is PPI the same as DPI?
They're related but not identical. PPI describes pixels on a screen; DPI (dots per inch) describes ink dots when printing. People often use the terms interchangeably, but a display spec is really PPI.
Why does dot pitch matter?
Dot pitch is the physical gap between pixels. A smaller pitch means finer detail and smoother edges. It's handy when comparing two screens, since it captures sharpness in a single millimetre figure.