Pixel Density Calculator
Calculate PPI, DPI, pixel pitch, and physical screen dimensions from resolution and diagonal size.
Width: 20.74 in (52.7 cm)
Height: 11.67 in (29.6 cm)
Total Pixels: 2.07 Megapixels
Distance: 3.1 ft (0.94 m)
At this distance or further, a person with 20/20 vision cannot distinguish individual pixels.
A pixel pitch of 0.274 mm means there are 36 pixels packed into every centimetre of the screen.
How pixel density (PPI) is calculated
PPI (pixels per inch) is calculated from the screen resolution and physical size: PPI = √(width² + height²) / diagonal. A higher PPI means more pixels packed into each inch, resulting in sharper text and images. Apple's "Retina" displays are typically 220+ PPI for Macs and 400+ PPI for iPhones.
PPI measures the physical pixel density; "logical DPI" used in CSS is usually 96 dpi on most operating systems. For CSS pixel sizing, try the px to rem converter.
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Working out a display's PPI from its resolution and diagonal size.
- Comparing two screens on actual pixel density rather than resolution alone.
- Checking whether an asset has enough pixels for a given physical size.
- Deciding what resolution to export at for a known display.
- Understanding why one screen looks sharper than another at the same resolution.
Frequently Asked Questions
- How is PPI calculated?
- The diagonal resolution in pixels divided by the diagonal in inches — so the pixel diagonal comes from Pythagoras on the width and height. A 2560×1440 27-inch panel works out at about 109 PPI, which is why the arithmetic needs both dimensions rather than just one.
- What density looks sharp?
- It depends on viewing distance, because what matters is angular resolution. Roughly 110 PPI is acceptable at desk distance, 160 is comfortable, and above 220 is where individual pixels stop being resolvable — which is why a phone needs far more PPI than a monitor.
- What does Retina actually mean?
- A marketing term for a density where a typical viewer cannot distinguish pixels at the normal distance for that device. That is why the threshold differs by product — around 220 PPI for a laptop and over 300 for a phone held much closer.
- How does PPI relate to device pixel ratio?
- It does not directly. DPR is the ratio of hardware pixels to CSS pixels and is set by the operating system, usually to a round number. A 163 PPI display and a 220 PPI one can both report a DPR of 2, which is why CSS layout does not vary with physical density.
- Is higher density always better?
- It costs battery and GPU throughput to drive, and past the resolvable limit it buys nothing visible. Beyond roughly 300 PPI on a phone the tradeoff is measurably negative, which is why flagship densities plateaued rather than continuing to climb.
Common errors and gotchas
- Comparing resolution without size, where the same pixel count is dense on a phone and coarse on a television.
- Confusing PPI with the device pixel ratio, which is a software scaling factor.
- Assuming higher PPI always looks sharper, when viewing distance matters just as much.
- Using the screen diagonal as a width, which needs the aspect ratio to separate.
- Applying a screen PPI figure to print, where the requirements are entirely different.