Monitor PPI Calculator
Calculate your monitor pixels per inch (PPI) from screen size and resolution.
Find optimal viewing distance and compare to Retina display PPI standards.
How Monitor PPI Is Calculated
PPI (Pixels Per Inch) measures the pixel density of a display — how many pixels fit into one inch of screen space. Higher PPI means sharper images and crisper text, but the perceptible benefit diminishes beyond a certain viewing distance.
PPI formula:
PPI = √(Horizontal pixels² + Vertical pixels²) ÷ Screen diagonal (inches)
The diagonal pixel count is calculated using the Pythagorean theorem across the resolution.
Worked example — 27-inch 4K monitor (3840 × 2160):
Diagonal pixels = √(3840² + 2160²) = √(14,745,600 + 4,665,600) = √19,411,200 = 4,405.8 pixels
PPI = 4,405.8 ÷ 27 = 163.2 PPI
Common monitor PPI values:
| Display | Resolution | Size | PPI |
|---|---|---|---|
| 27" 1080p | 1920×1080 | 27" | 81.6 |
| 27" 1440p | 2560×1440 | 27" | 108.8 |
| 27" 4K | 3840×2160 | 27" | 163.2 |
| 24" 1080p | 1920×1080 | 24" | 91.8 |
| 15.6" laptop 1080p | 1920×1080 | 15.6" | 141.2 |
| iPhone 15 (OLED) | 2556×1179 | 6.1" | 460 |
Retina threshold (Apple’s definition):
Apple defines “Retina” as the PPI at which individual pixels become indistinguishable at typical viewing distance. The threshold varies by device:
- Smartphone (12 inches viewing distance): ~300 PPI
- Tablet (15 inches): ~220 PPI
- Desktop monitor (24 inches): ~110 PPI
- Living room TV (10 feet): ~40–60 PPI
The 1°/60 arcminute rule:
Critical PPI = 3,438 ÷ Viewing distance (inches)
At 24 inches, critical PPI = 3,438 ÷ 24 = 143 PPI. A 4K 27-inch monitor at 163 PPI exceeds this threshold — pixels are invisible to 20/20 vision at that distance.