PPI Calculator
Enter the resolution and diagonal to get the pixel density in PPI.
What this tool does
PPI is the diagonal length in pixels divided by the diagonal in inches. A 24-inch 1920 × 1080 screen has a diagonal of 2,202.9 pixels, so 2,202.9 ÷ 24 = 91.8 PPI and a pixel pitch of 0.277 mm. Enter your own resolution and screen size above.
Applies the pixel density formula to a resolution and a screen diagonal.
Gives the dot pitch, physical dimensions, aspect ratio and megapixels.
How to use it
- Enter the horizontal and vertical resolution in pixels.
- Enter the screen diagonal in inches.
- Read the pixel density and dot pitch.
- Use the size and aspect ratio to check the screen shape.
Why use this calculator
Calculates pixels per inch, dot pitch, physical width and height, aspect ratio and megapixels from a resolution and a diagonal size. Two screens with the same resolution can look very different if one is larger. Pixel density tells you how sharp text and images will look at a given size, which is useful when comparing monitors and phones.
Why we built it
We built the PPI calculator to give pixel density, dot pitch and physical size from a resolution and diagonal. Size print and web images with the image size calculator and the aspect ratio calculator.
Handy alongside this: the Coffee Ratio Calculator.
Related tools worth a look: the Online Ruler.
Who this tool is for
- Shoppers comparing monitors and phones
- Designers and developers
- Students learning about display density
When to use it
- Choosing a monitor or a laptop.
- Comparing phone screens.
- Designing for a given display.
- Checking if a display is retina-class.
How it works
Diagonal in pixels = √(width² + height²). PPI = diagonal in pixels ÷ diagonal in inches. Dot pitch = 25.4 mm ÷ PPI. The physical width is diagonal × width ÷ diagonal in pixels, and similarly for height.
Examples: 1920 × 1080 at 24 in is 91.8 PPI; 3840 × 2160 at 27 in is 163.2 PPI; 2556 × 1179 at 6.1 in is about 460 PPI.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Horizontal resolution | 1920 |
| Vertical resolution | 1080 |
| Screen diagonal | 24 |
With those inputs, the calculator returns:
- Pixel density: 91.8 PPI
- Dot pitch (pixel size): 0.2767 mm
- Screen width: 20.92 in (53.1 cm)
- Screen height: 11.77 in (29.9 cm)
- Screen area: 246.1 sq in
- Aspect ratio: 16:9
- Megapixels: 2.07
- Pixels per cm: 36.1
What you give it, and what you get back
| Item | Details |
|---|---|
| Resolution | Width and height in pixels. |
| Diagonal | Screen size in inches. |
| Output | PPI, dot pitch, width, height, area, aspect ratio, megapixels and a description. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Result differs from the spec sheet | The advertised diagonal is rounded. | Use the exact diagonal if known. |
| I need print DPI | PPI describes a screen. | Use the image size calculator for print. |
| Aspect ratio odd | Not a standard shape. | Check the resolution. |
Assumptions and limitations
- Treats pixels as square.
- Does not account for sub-pixel layout or scaling.
Frequently asked questions
What is PPI?
Pixels per inch: how many pixels fit in a line one inch long on a screen.
How do I calculate PPI?
Divide the diagonal in pixels by the diagonal in inches.
What is a good PPI?
Around 100 is standard, 150 or more is sharp at desktop distance and 300 or more is retina-class on phones.
What is the difference between PPI and DPI?
PPI describes display pixels; DPI describes printer dots or the print resolution of an image.
What is dot pitch?
The size of one pixel, 25.4 mm divided by PPI.
Is my text or file sent anywhere?
No. Everything runs in your browser and nothing leaves the page.
Sources and accuracy
Pixels per inch is the diagonal pixel count, the square root of width squared plus height squared, divided by the screen diagonal in inches, the standard definition used for display density. Millimetre to inch conversions use NIST factors, and reference pixel sizing for screens is defined by the World Wide Web Consortium.
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.