Display Pixel Density (PPI)

What the PPI Calculator Does

This tool calculates pixel density, measured in pixels per inch (PPI), for any flat screen. You enter the horizontal and vertical resolution in pixels and the diagonal screen size in inches, and it returns how tightly packed the pixels are on that display.

PPI is useful for anyone comparing monitors, phones, laptops, or TVs. Designers and developers use it to judge how sharp text and images will look, gamers and shoppers use it to compare panels at different sizes, and DIY builders use it to confirm a replacement panel matches the original.

How PPI Is Calculated (The Formula)

Resolution describes width and height in pixels, but a screen's size is given as a diagonal measurement. To match the two, you first find the diagonal length in pixels using the Pythagorean theorem, then divide by the physical diagonal in inches:

ppi = hypot(wPx, hPx) / diagonalInches = sqrt(wPx^2 + hPx^2) / diagonalInches

Here wPx and hPx are the horizontal and vertical pixel counts. The hypot() function is just shorthand for the square root of the sum of the squares, which gives the diagonal resolution in pixels. Dividing that diagonal pixel count by the diagonal inches yields pixels per inch.

Worked Example: A 27-inch 1440p Monitor

Take a common 27-inch monitor with a 2560 x 1440 (QHD) resolution. Plug the numbers into the formula step by step:

• Square each dimension: 2560^2 = 6,553,600 and 1440^2 = 2,073,600.
• Add them: 6,553,600 + 2,073,600 = 8,627,200.
• Take the square root for the diagonal in pixels: sqrt(8,627,200) approx 2937.2.
• Divide by the diagonal inches: 2937.2 / 27 approx 108.8 PPI.

Reading the Result and Common Reference Points

Higher PPI means smaller, denser pixels and a sharper image at a given distance. The same resolution looks sharper on a smaller screen because the pixels are squeezed into less space.

For context, a 27-inch 1440p panel lands near 109 PPI, a 24-inch 1080p monitor is about 92 PPI, and a 27-inch 4K (3840 x 2160) screen reaches roughly 163 PPI. Phones run far higher, often 400 to 500+ PPI, because they are viewed up close on a tiny diagonal.

Tips and Common Mistakes

A few details change the answer or how you should interpret it. Keep these in mind:

• Use the diagonal, not the width. Screen sizes are always quoted as the corner-to-corner diagonal, so do not enter the horizontal measurement by mistake.
• Match the aspect ratio. The diagonal-in-pixels step already accounts for shape, so an ultrawide 21:9 panel and a 16:9 panel can share a diagonal size but differ in PPI.
• PPI is not DPI. PPI describes screen pixels; DPI describes printer dots. The terms are often swapped, but they measure different things.
• Viewing distance matters. A 50 PPI TV can look crisp from across a room, while a 300 PPI phone is judged from inches away, so compare PPI within the same use case.
• Use native resolution. Enter the panel's actual pixel count, not a scaled or downsampled setting, or the result will be wrong.