How to Calculate PPI
What is PPI?
PPI (Pixels Per Inch) measures screen resolution density — how many pixels fit in one linear inch of a display. Higher PPI means sharper text and images. Apple branded 326+ PPI as 'Retina' — the point where individual pixels become indistinguishable at normal viewing distance.
Step-by-Step Guide
- 1PPI = √(width² + height²) / diagonal screen size (inches)
- 2Diagonal pixels = √(horizontal_res² + vertical_res²)
- 3Retina threshold ≈ 300 PPI at ~12 inch viewing distance
- 4Effective viewing PPI depends on viewing distance
Worked Examples
Input
iPhone 15: 2556×1179 pixels, 6.1" display
Result
460 PPI
Super Retina XDR
Input
1920×1080 monitor, 24"
Result
91.8 PPI
Standard 1080p desktop
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