DPI and PPI Calculator

Pixel density is what makes one screen look razor sharp and another look coarse, even at the same resolution, and this calculator measures it for you. Enter a display's horizontal and vertical resolution in pixels along with its diagonal size in inches, and it returns the pixels per inch, or PPI, together with the dot pitch, the distance between pixels in millimetres. PPI matters because it describes how tightly the pixels are packed: the same 1920 by 1080 resolution looks crisp on a small laptop screen but visibly blocky stretched across a large television, because the pixels are spread further apart. The calculation uses Pythagoras to find the diagonal in pixels, the square root of the width squared plus the height squared, then divides by the diagonal in inches to give the density. The dot pitch is simply the inverse, the physical size of each pixel, which is useful in signage, engineering and any work where you care about the real-world size of a pixel. Knowing the PPI helps you compare displays fairly when shopping, judge whether text and images will look sharp at a normal viewing distance, design interfaces that scale well across devices, or work out how close you can sit to a screen before the pixels become visible. Phones today often pack well over 400 PPI, desktop monitors commonly sit between 90 and 160, and large televisions can drop below 50, which is why they are made to be viewed from across the room. Although DPI and PPI are often used interchangeably, PPI is the correct term for screens, while DPI properly belongs to printers. The formula and a worked example are explained clearly below.

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