PPI calculator and pixels per inch calculator

What PPI means

Pixels Per Inch (PPI) represents a measurement of display pixel density. It describes the number of physical pixels packed into one diagonal inch of screen space. A higher pixel density means the individual pixels are smaller and closer together, which makes text and image boundaries look much sharper.

Unlike digital image files that specify dimensions in pixels without a fixed physical scale, a physical screen has a fixed pixel grid. Our online pixel density calculator computes this density to show how clearly a screen can display fine details. If you don't know your current display dimensions, run a live display resolution test first to get the numbers you need.

How the PPI formula works

To calculate the pixel density of a screen, you need the horizontal resolution, vertical resolution, and diagonal screen size. First, you calculate the diagonal resolution in pixels using the Pythagorean theorem. Then, you divide that diagonal pixel count by the diagonal physical screen size in inches.

In this math formula, w represents the horizontal pixel width, h represents the vertical pixel height, and d represents the physical diagonal size in inches. The result shows how many physical screen pixels populate each physical inch.

Why pixel density matters

How to interpret PPI by device type

Different types of screens target different pixel density ranges depending on how close you sit to them. Desktop monitors usually look sharpest between 90 and 120 PPI because you sit about an arm's length away. Laptops are viewed closer, so they require a higher range between 120 and 220 PPI to hide individual pixels.

Mobile phones are held closest to your eyes and target high densities between 300 and 500 PPI. At these high numbers, the screen achieves what is commonly called a Retina display standard. You can look up exact PPI figures for hundreds of devices in the smartphone resolution database. Displays that fall below these ranges can look pixelated, making text look jagged and hard to read. On very high PPI screens like 4K phones, individual pixels become nearly invisible — which also makes spotting a dead pixel much harder than on a standard 1080p monitor.

Why viewing distance matters

Your physical distance from a screen determines whether you can see the individual physical pixels. The human eye cannot resolve separate pixels if the screen density is high enough for a given distance. For this reason, a 55-inch 4K TV viewed from across a living room looks perfectly sharp, even though its density is under 80 PPI.

However, that same 80 PPI density would look blurry on a phone because you view a phone from just a few inches away. As you move closer to a screen, the required pixel density to maintain a sharp appearance increases. Designers use these viewing principles to choose the correct screen specifications for different hardware setups.

PPI vs resolution vs DPR

Screen resolution specifies the total physical pixel grid of a display, such as 1920 by 1080. PPI measures the density of these pixels, combining the resolution with the physical screen size. The device pixel ratio (DPR) is a scaling factor that tells the browser how many physical pixels should render one logical CSS layout pixel.

A high-PPI display often uses a higher DPR to scale up text and UI elements so they do not look tiny. For example, a 4K laptop screen has a high PPI and uses scaling to keep layouts readable. You can read our detailed guide comparing viewports vs resolutions vs DPR to see how these metrics interact.

Common displays and their pixel densities

Here is a reference guide mapping standard resolutions, aspect ratios, and physical sizes to their exact PPI values:

Related tools and guides

If you want to check other screen parameters, browse our collection of display tools. You can check your pixel ratio using our DPR checker, or measure your layout size with our viewport size checker. To understand print resolution, read our guide explaining DPI vs PPI differences.

Frequently asked questions