Last updated: March 2026
What Is the PPI Calculator?
The PPI Calculator is a free tool that calculates the pixel density (pixels per inch) of any display from its resolution and physical size. Over 200,000 designers and developers search for PPI calculators monthly when choosing monitors, designing responsive interfaces, or creating assets at the correct resolution for different devices. Enter your screen's resolution and diagonal size to see its PPI, how it compares to popular devices, and what asset resolution (@1x, @2x, @3x) you should design for.
Unlike basic calculators that only show a PPI number, this tool also provides dot pitch, aspect ratio, physical dimensions, a device comparison table, and actionable design recommendations. Whether you are evaluating a new monitor purchase, optimizing images for a specific display, or building responsive layouts, the PPI Calculator gives you everything you need in one place.
How to Calculate PPI
Enter the screen's pixel width and height plus the diagonal measurement in inches. The calculator computes PPI using the Pythagorean theorem: it first finds the diagonal pixel count as the square root of width squared plus height squared, then divides by the diagonal size in inches. The result is your display's pixel density.
From the PPI value, the tool derives additional metrics. Dot pitch is calculated as 25.4 divided by PPI, giving you the physical size of each pixel in millimeters. The aspect ratio is simplified using the greatest common divisor. Physical width and height are computed from the diagonal and aspect ratio using trigonometry.
The calculator then categorizes your display: Standard (below 150 PPI), High Density (150–250 PPI), HiDPI / Retina (250–400 PPI), or Super Retina (400+ PPI). You can use the quick presets dropdown to instantly load specifications for popular devices like the iPhone 16 Pro, MacBook Pro, Samsung Galaxy S24, and common desktop monitors.
Understanding Display Density
Display density determines how sharp text, images, and UI elements appear on screen. A higher PPI means more pixels are packed into each inch, producing smoother edges and finer detail. This is why a 4K monitor at 27 inches (163 PPI) looks noticeably sharper than the same resolution stretched across 32 inches (138 PPI).
For designers and developers, PPI directly affects asset creation workflows. Standard-density displays need @1x assets, while Retina displays require @2x or @3x versions to avoid blurry rendering. The device comparison table shows exactly where your display falls relative to the most popular phones, tablets, laptops, and monitors on the market, so you can make informed decisions about which asset resolutions to support.
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.