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Calculate screen pixel density from resolution and diagonal size. Essential for display comparison and understanding screen quality.
Quick Device Presets:
Calculation Formula:
diagonal_px = √(width² + height²)
DPI = diagonal_px ÷ diagonal_inches
Example: √(1920² + 1080²) ÷ 24 ≈ 91.79 DPI
Retina Display Standard
Apple's "Retina" displays have pixel densities where individual pixels are indistinguishable at normal viewing distance (typically 220+ PPI for laptops, 326+ PPI for phones).
| Device | Resolution | Diagonal | DPI | Category |
|---|---|---|---|---|
| iPhone 15 Pro | 1179 × 2556 | 6.1" | 460 | XXXHDPI |
| iPhone 15 Pro Max | 1290 × 2796 | 6.7" | 460 | XXXHDPI |
| Samsung Galaxy S24 | 1080 × 2340 | 6.2" | 416 | XXHDPI |
| iPad Pro 12.9" | 2048 × 2732 | 12.9" | 264 | XHDPI |
| MacBook Pro 16" | 3456 × 2234 | 16.2" | 254 | XHDPI |
| MacBook Air 13" | 2560 × 1664 | 13.6" | 224 | HDPI |
| Dell XPS 15 | 3840 × 2400 | 15.6" | 282 | XHDPI |
| 4K TV (55") | 3840 × 2160 | 55" | 80 | LDPI |
| Full HD Monitor (24") | 1920 × 1080 | 24" | 92 | LDPI |
| 4K Monitor (27") | 3840 × 2160 | 27" | 163 | HDPI |
DPI (Dots Per Inch) and PPI (Pixels Per Inch) measure pixel density - how many pixels fit in one inch of screen space. Higher pixel density means sharper, more detailed images. For displays, PPI is the technically correct term, but DPI is often used interchangeably. The calculation uses the Pythagorean theorem to find the diagonal pixel count, then divides by the physical diagonal measurement.
"Retina" is Apple's marketing term for displays where individual pixels cannot be distinguished at typical viewing distances. This varies by device: phones need 326+ PPI (held 10-12 inches away), laptops need 220+ PPI (18-24 inches), and desktop monitors need 110+ PPI (24-30 inches). The concept is based on the human eye's resolving power of approximately 1 arcminute (1/60th of a degree).
Higher pixel density creates sharper text, smoother curves, and more detailed images. It's crucial for reading comfort, photo editing, graphic design, and video content. Modern smartphones have very high pixel densities (400+ PPI) because they're viewed up close. Laptops typically have 200-300 PPI, while desktop monitors have 90-180 PPI since they're viewed from further away. Large TVs may have low DPI (50-100) but still look sharp because of viewing distance.
Use the formula: DPI = √(width² + height²) ÷ diagonal_inches. First, calculate the diagonal pixel count using the Pythagorean theorem: √(width² + height²). Then divide by the physical diagonal size in inches. For example, a 1920×1080 screen with 24" diagonal: √(1920² + 1080²) ÷ 24 = 91.79 DPI.
PPI (Pixels Per Inch) is the correct term for digital displays - it measures pixel density. DPI (Dots Per Inch) technically refers to printer resolution. However, both terms are commonly used interchangeably for screens. In the context of displays, they mean the same thing: how many pixels fit in one inch.
For desktop monitors: 90-110 DPI is standard (24" Full HD), 140-180 DPI is high quality (27" 4K), and 200+ DPI is premium (Retina-class). For laptops: 130-150 DPI is good, 200-250 DPI is excellent (MacBook Pro, Dell XPS). For smartphones: 300+ PPI is standard, 400+ PPI is high-end. Higher isn't always better - consider viewing distance and use case.
Not necessarily. Higher DPI provides sharper images but requires more processing power, can make UI elements too small without scaling, and consumes more battery on mobile devices. The optimal DPI depends on viewing distance: smartphones benefit from 400+ PPI (viewed close), monitors are fine with 100-180 PPI (viewed at arm's length), and TVs work well with 50-100 PPI (viewed from across the room).
"Retina" isn't a fixed DPI value - it depends on viewing distance. Apple uses: 326 PPI for iPhones (10" viewing distance), 264 PPI for iPads (15" distance), and 220 PPI for MacBooks (20-24" distance). The principle is that pixels should be indistinguishable at typical viewing distance. Generally, 220+ PPI for laptops, 326+ PPI for phones, and 260+ PPI for tablets qualify as "Retina-class" displays.