Enter your resolution and screen size to calculate pixels per inch (PPI), dot pitch, and the true physical dimensions of your display. Free and instant.
Your display
The screen's advertised diagonal, e.g. 24 or 27 inches.
Result
Pixel density (PPI)
—
Dot pitch—
Physical size—
Total pixels—
Sharpness—
What PPI means
PPI (pixels per inch) is how many pixels your screen packs into each inch of its surface. Higher PPI means finer detail and smaller, sharper text. It is calculated from the diagonal pixel count divided by the physical diagonal:
PPI = √(width² + height²) ÷ diagonal inches
A 24-inch 1920×1080 monitor works out to about 92 PPI, while a 27-inch 4K panel is around 163 PPI. Phones often exceed 400 PPI. Anything above roughly 220 PPI at normal viewing distance looks "retina" sharp, meaning individual pixels are hard to see.
Why it matters
PPI is exactly what an online ruler has to account for. Because two screens can show the same 1920×1080 image at very different physical sizes, a "1 cm" line is only truly 1 cm after you calibrate for your screen's real pixel density. Knowing your PPI also helps you judge whether a monitor's text will look crisp before you buy it.
Frequently Asked Questions
On Windows, open Settings, then System, then Display, and read Display resolution. On a Mac, open System Settings, then Displays. Phone and tablet resolutions are listed on the manufacturer's spec page.
For a desktop monitor viewed at arm's length, 90 to 110 PPI is standard and 140 or more looks noticeably sharper. Laptops and phones benefit from 200 PPI and up because you hold them closer.
Not quite. PPI describes pixels on a screen; DPI (dots per inch) describes dots of ink on printed paper. People use the terms interchangeably, but for printing you want the DPI calculator.
Beyond about 220 PPI at typical viewing distance the human eye cannot resolve individual pixels, so extra density gives diminishing returns while using more power and performance.