Free tool
PPI Calculator: Pixel Density from Resolution and Screen Size
Enter the width and height in pixels and the diagonal size, and the calculator returns how sharp the screen is and how big it is in real units. Presets cover common monitors, laptops, a phone and a TV, and a button fills in the resolution of the screen you are on.
Presets are examples of common sizes; check your own model's specs.
The sums are done in your browser and nothing is sent anywhere. Your last inputs are remembered on your own device, and the share link puts them in the part of the address after the hash sign.
A question that comes up before a design review
A designer asks why the layout looks crisp on one monitor and soft on another. A buyer compares two displays that have the same resolution but different sizes. A team wants to know how large a screen really is before planning a kiosk or a dashboard wall. All three questions come down to pixel density, which is the number of pixels packed into one inch of the screen.
Pick a preset or type your own figures. The result cards update at once, and the first card is the headline: pixels per inch, with the same figure per centimetre underneath.
What each result card means
| Card | How it is worked out |
|---|---|
| Pixels per inch | The diagonal in pixels, which is the square root of width squared plus height squared, divided by the diagonal in inches |
| Dot pitch | 25.4 millimetres divided by the PPI, the distance between neighbouring pixel centres |
| Width and Height | The diagonal is split in the proportion of the two pixel counts, then shown in inches and centimetres |
| Screen area | Width times height, in square inches and square centimetres |
| Aspect ratio | Width and height divided by their greatest common divisor |
| Total pixels | Width times height, in megapixels and as a full count |
| Pixels blend from | The distance at which one pixel covers one arcminute of vision |
A worked example: a screen of 1920 by 1080 pixels has a diagonal of about 2203 pixels. On a 24 inch diagonal that is about 91.8 pixels per inch. The same pixel count on a 27 inch diagonal gives a lower figure, because the same pixels are spread over more space.
Getting the inputs right
- Resolution is the native pixel grid, not a scaled setting. Use the resolution from the specification sheet, or press the button that fills in your own screen's current resolution.
- Diagonal is the corner to corner size of the visible area. Choose inches or centimetres in the unit menu.
- A browser cannot know the physical size of the display it is on, so that is the one number you always type yourself.
- The presets are examples of common sizes. Check the exact specification of your own model before relying on the result.
The button for your own screen multiplies the screen width and height the browser reports by the device pixel ratio. On a scaled display that gives the physical pixel count, but check it against the specifications if the figure looks odd.
Reading the blend distance with care
The last card estimates how far away you must sit before single pixels stop being separate to the eye. It uses an angle of one arcminute, a common figure for sharp eyesight. Real viewing depends on your eyes, the content and the screen type, so treat the distance as a rough guide and not a limit.
PPI describes a screen, not a picture file. If you are preparing a file for printing, the related measure is the density stored in the image, and the change image DPI tool on this site writes that value. A picture on screen is shown at its pixel size no matter what density is stored in it.
Why site owners should care
High density screens show a one-pixel line as a fine line, and show a blurry logo as a blurry logo. If your images look soft on newer phones and laptops, they may need larger source files. Our website optimization and conversion improvements work includes checking images against real screens, so that sharpness and page weight stay in balance.
Frequently asked questions
How do I calculate PPI?
Take the square root of the width in pixels squared plus the height in pixels squared. Divide that by the diagonal in inches. The calculator does this for you and also shows the figure per centimetre.
Is PPI the same as DPI?
They are often mixed up. PPI counts pixels on a screen or in a picture, while DPI counts printed dots per inch. This page works out PPI for displays.
Can the page detect my screen size in inches?
No. A browser can report pixels but not the physical size of the glass, so you type the diagonal from your device specifications.
Why do two screens with the same resolution give different results?
Because PPI depends on size too. The same grid of pixels on a bigger screen is spread out more, so the number drops.
What is dot pitch?
It is the distance between the centres of two neighbouring pixels, shown here in millimetres. A smaller value means a finer grid.
Can I share a result?
Yes. Copy link makes an address with your numbers in it, and Copy result copies a one-line summary.
More free tools
- screen resolution checker: See your screen size in real pixels, the pixel ratio, window and page area, and an aspect ratio.
- Change image DPI: Write a new DPI into JPG and PNG files, or resample a picture to a print size.
- Aspect ratio calculator: Find a ratio, resize without distortion, and work out crops or bars for a new shape.
- online ruler: An on-screen ruler in cm or inches set to true size with a bank card, with a printable PDF ruler.
- image resizer: Resize pictures by pixels or percent with fit, crop or stretch, presets and file type choices.