PPI (Pixels Per Inch) Calculator
Calculate display PPI pixels per inch from width, height, and screen size. It also shows aspect ratio for comparing monitors and devices.
PPI (Pixels Per Inch) Calculator
Result will appear here...
What this does
So you want to know how sharp a display is, or compare two of them fairly, and that comes down to pixel density, the pixels packed into each inch. This works it out. Enter the resolution in pixels and the screen's diagonal size, and it gives you the PPI along with the aspect ratio and a few related figures.
How to use it
- Enter the screen width and height in pixels, for example 1920 and 1080.
- Enter the diagonal screen size, and choose inches or centimetres.
- Press Calculate to see the PPI and the rest of the breakdown.
How it works
PPI, pixels per inch, is the pixel density of a display, and there is a clean formula for it. You take the diagonal length of the screen in pixels, worked out from the width and height, and divide it by the diagonal size in inches:
PPI = √(width^2 + height^2) ÷ diagonal
The top half uses Pythagoras to turn the width and height in pixels into the diagonal in pixels, and dividing by the physical diagonal gives the pixels per inch. The tool does this for you, converting your diagonal to inches first if you entered centimetres, and also reports the aspect ratio, the physical width and height, and the total megapixels.
A worked example
Take a 15 inch laptop screen at 1920 by 1080. The diagonal in pixels is √(1920^2 + 1080^2), which is about 2203 pixels, and dividing that by 15 inches gives roughly 147 PPI. A 27 inch monitor at the same 1920 by 1080 spreads those pixels over a bigger area, so its PPI drops to about 82, which is why it looks less sharp up close. That is the whole value of PPI: it lets you compare displays of different sizes and resolutions on equal terms.
What PPI tells you
A higher PPI means finer detail and crisper text, which is why phones, with small screens and high resolutions, have far higher PPI than most desktop monitors. One thing the number does not capture is viewing distance: a billboard has a very low PPI but looks fine because you stand far from it, while a phone is held inches from your eyes. For comparing screens you use at a similar distance, though, PPI is the fair measure.
Questions people ask
What is a good PPI?
It depends on how close you sit. Phones are often above 400 PPI, laptops and high resolution monitors commonly sit between 100 and 220, and a large screen viewed from a distance can look fine much lower. Higher means sharper at the same distance.
Why do two screens with the same resolution have different PPI?
Because PPI depends on size as well as resolution. The same pixel count spread over a larger screen gives a lower density, so a big monitor and a small laptop at 1920 by 1080 have very different PPI.
Can I enter the diagonal in centimetres?
Yes. Choose centimetres next to the diagonal field and the tool converts it to inches before calculating.
What is the aspect ratio it shows?
It is the width to height ratio in its simplest form, like 16:9, found by reducing your width and height by their greatest common divisor.
References
- Wikipedia. Pixel density. https://en.wikipedia.org/wiki/Pixel_density
- Wikipedia. Display aspect ratio. https://en.wikipedia.org/wiki/Display_aspect_ratio
Sugam Baskota is a senior software engineer and Computer Science graduate from UT Arlington, with interests in user scripts, browser extensions, developer tooling, and productivity systems. He spends time building practical utilities and extensions in the kinds of workflows Eon is designed to simplify. At Eon Tools, he reviews useful, password, and developer tools.