PPI (Pixel Density) Calculator
Enter a screen's resolution and diagonal size to calculate its pixel density (PPI) — pixels per inch — a key measure of how sharp text and images appear on that display.
How the PPI (Pixel Density) formula works
Pixel density from resolution and physical screen size:
Diagonal pixels = √(Width px² + Height px²) PPI = Diagonal pixels / Diagonal size (inches)
Step-by-step calculation
- Calculate the diagonal resolution in pixels using the Pythagorean theorem on width and height.
- Divide by the screen's physical diagonal size in inches.
Worked example
A 6.1-inch phone screen at 1170×2532 resolution: Diagonal pixels = √(1170² + 2532²) ≈ 2,789. PPI = 2,789 / 6.1 ≈ 457 — a very high-density display.
Frequently asked questions
What PPI is considered 'sharp' to the human eye?
Roughly 300 PPI or higher is commonly cited as the point where individual pixels become imperceptible at typical smartphone viewing distance — sometimes called 'Retina' quality, a term popularized by Apple, though the exact perceptible threshold depends on viewing distance.
Why do larger screens often have lower PPI at the same resolution?
PPI depends on both resolution and physical size — spreading the same number of pixels across a larger screen area reduces how densely packed they are, which is why a large TV can have a much lower PPI than a small phone despite similar or higher raw resolution.