Screen Resolution Calculator
Calculate pixels per inch (PPI) from screen resolution and diagonal size. Compare devices and check Retina/HiDPI thresholds.
Quick Answer
PPI = sqrt(width² + height²) / diagonal inches. A 27-inch 4K monitor (3840x2160) has 163 PPI. Apple considers 200+ PPI as Retina for laptops, 300+ for phones.
Screen Details
Results
163
PPI (Pixels Per Inch)
Yes
Retina / HiDPI (Monitor (150+ PPI))
8.3 MP
Total Megapixels
16:9
Aspect Ratio
Device Comparison
| Device | Resolution | Size | PPI |
|---|---|---|---|
| iPhone 15 | 2556x1179 | 6.1" | 461 |
| MacBook Pro 14″ | 3024x1964 | 14.2" | 254 |
| 27″ 4K | 3840x2160 | 27" | 163 |
| 32″ 4K | 3840x2160 | 32" | 138 |
| 24″ 1080p | 1920x1080 | 24" | 92 |
| iPad Pro 12.9″ | 2732x2048 | 12.9" | 265 |
About the Screen Resolution Calculator
PPI (Pixels Per Inch) measures pixel density, which determines how sharp text and images appear on a screen. Higher PPI means sharper display at the same viewing distance. This calculator computes PPI from any screen resolution and physical size, and tells you whether the display qualifies as Retina or HiDPI based on the device category.
Understanding PPI
PPI is calculated by dividing the diagonal resolution in pixels by the diagonal screen size in inches. The diagonal pixel count is the square root of (width squared + height squared). A 27-inch 4K monitor (3840x2160) has about 163 PPI. A 6.1-inch iPhone 15 (2556x1179) has about 460 PPI. The same resolution on a larger screen has lower PPI and appears less sharp at close viewing distances.
What Is Retina Display?
Apple coined the term "Retina" to describe displays where individual pixels are not visible at normal viewing distance. For phones held at 10-12 inches, this threshold is about 300 PPI. For laptops at 18-20 inches, about 200 PPI. For desktop monitors at 24-30 inches, about 150 PPI. The further you sit from a screen, the lower the PPI needed for the display to appear sharp to the human eye.
Choosing the Right Monitor
For general office work, a 24-inch 1080p monitor (92 PPI) is adequate. For programming and design, a 27-inch 4K monitor (163 PPI) provides excellent text clarity and workspace. For photo and video editing, color accuracy matters more than PPI alone. For gaming, consider refresh rate (144Hz+) alongside resolution. The sweet spot for most professionals is 27-inch 4K or 32-inch 4K, balancing pixel density with usable screen real estate.
HiDPI Scaling
High-PPI displays often use scaling to keep interface elements at readable sizes. A 4K monitor at 27 inches typically uses 150% or 200% scaling, meaning a 4K display at 200% scale shows the same amount of content as a 1080p display but with four times the pixel detail. macOS and Windows handle this differently, with macOS generally offering smoother HiDPI rendering for non-native applications.
PPI vs DPI
PPI (Pixels Per Inch) refers to screen displays. DPI (Dots Per Inch) refers to print output. While often used interchangeably, they measure different things. A 300 DPI print means 300 ink dots per inch on paper. A 300 PPI screen means 300 pixels per inch on the display. For web and screen design, PPI is the relevant metric. For print design, DPI matters more when preparing files for output.