Last updated: March 2026
What Is the Pixel Density Calculator?
The Pixel Density Calculator is a free tool that calculates the PPI (pixels per inch) of any display from its resolution and physical size. Designers, developers, and tech enthusiasts use it when choosing monitors, designing responsive interfaces, or creating assets at the correct resolution for different devices.
Enter your screen's pixel width and height along with its diagonal size in inches. The calculator instantly shows PPI, dot pitch, aspect ratio, physical dimensions, a density category, and a comparison table against popular devices from phones to desktop monitors.
How Pixel Density Is Calculated
Pixel density is computed using the Pythagorean theorem. The diagonal pixel count equals the square root of the width squared plus the height squared. Dividing this by the diagonal size in inches gives you PPI. From there, dot pitch (25.4 / PPI) tells you how large each pixel is in millimeters.
The calculator categorizes displays into four tiers: Standard (below 150 PPI), High Density (150–250 PPI), HiDPI / Retina (250–400 PPI), and Super Retina (400+ PPI). Each category comes with specific asset recommendations so you know whether to use @1x, @2x, or @3x images in your designs.
Frequently Asked Questions
What PPI is considered "Retina"?
Apple's "Retina" threshold is when individual pixels are indistinguishable at typical viewing distance — approximately 220+ PPI for laptops (arm's length), 300+ PPI for phones (hand distance). In practice, displays above 250 PPI are generally considered HiDPI/Retina.
Why does PPI matter for designers?
Higher PPI displays show finer detail. If you design at 1x resolution for a 2x Retina display, images and icons appear blurry. Knowing a device's PPI tells you what asset resolution to use (@1x, @2x, or @3x).
Is PPI the same as DPI?
PPI (pixels per inch) refers to screen displays. DPI (dots per inch) technically refers to printed output. In practice, they're used interchangeably for screens, though PPI is more accurate.
What's a good PPI for a desktop monitor?
For a desk monitor at arm's length (2-3 feet), 100-110 PPI is standard (1080p at 24"), 163 PPI is sharp (4K at 27"), and 220+ PPI is Retina-quality (5K at 27" or Apple Studio Display).
How do I find my screen's resolution and size?
On Windows: Settings → Display → Resolution. On Mac: Apple menu → About This Mac → Display. Physical size is usually listed in the monitor's spec sheet or marketing materials.