Monitor Resolution Calculator
A display's sharpness depends not just on its resolution but on how those pixels are spread across the screen. Pixels per inch ties the two together: it is the diagonal pixel count, found with the Pythagorean theorem, divided by the diagonal size in inches. From the same inputs you can read off the aspect ratio, the dot pitch, and the total megapixels. Enter the width and height in pixels and the diagonal in inches, and this calculator returns all four, with no estimation, just geometry.
Monitor resolution formula
Diagonal pixels = sqrt(width^2 + height^2)
PPI = diagonal pixels / diagonal inches
Aspect ratio = width : height (divided by their GCD)
Dot pitch (mm) = 25.4 / PPI
Total megapixels = width * height / 1,000,000
The diagonal pixel count uses the Pythagorean theorem. Dot pitch is the pixel spacing in millimeters, using 25.4 mm per inch.
Display context
- Higher PPI gives a sharper image; the comfortable level depends on viewing distance.
- Desktop monitors around 90 to 160 PPI look crisp at arm's length; phones exceed 400 PPI.
- 1920 by 1080 (Full HD) has an aspect ratio of 16:9 and about 2.07 megapixels.
- Dot pitch and PPI are reciprocals: smaller dot pitch means higher PPI and a finer image.
- Modern displays use square pixels, so diagonal PPI matches horizontal and vertical PPI.
Monitor resolution calculator: frequently asked questions
How is pixels per inch (PPI) calculated?
PPI is the diagonal resolution divided by the diagonal screen size in inches. The diagonal resolution is the square root of the width in pixels squared plus the height in pixels squared, by the Pythagorean theorem. Dividing that by the diagonal inches gives pixels per inch.
What is a good PPI for a monitor?
Higher PPI means a sharper image, but the comfortable viewing distance matters too. Phones often exceed 400 PPI because they are held close, while desktop monitors around 90 to 160 PPI look crisp at arm's length. This calculator reports the exact PPI so you can compare displays directly.
How is the aspect ratio found?
The aspect ratio is the width divided by the height, simplified to small whole numbers by dividing both by their greatest common divisor. For example 1920 by 1080 simplifies to 16:9. The calculator shows both the simplified ratio and the decimal width-to-height value.
What is dot pitch?
Dot pitch is the distance between the centers of adjacent pixels, the reciprocal of PPI converted to millimeters. It equals 25.4 divided by the PPI, since there are 25.4 millimeters in an inch. A smaller dot pitch means a finer, sharper display.
Why use the diagonal rather than width and height?
Screen sizes are quoted by diagonal, so PPI is defined against the diagonal for a like-for-like comparison. Because pixels are square on virtually all modern displays, the PPI computed from the diagonal matches the PPI you would get along the width or height.
Official sources
- NIST: Inch to millimeter conversion (25.4 mm per inch).
- U.S. Access Board: Display and information technology guidelines.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.