PPI Calculator (Pixels Per Inch)
Find a display’s pixel density from horizontal pixels, vertical pixels and diagonal size.
How the result changes
Only horizontal resolution changes; all other inputs stay at your current values. Each dot represents one whole-number input. This is not a forecast of real-world outcomes.
About this calculation
PPI Calculator (Pixels Per Inch): Find a display’s pixel density from horizontal pixels, vertical pixels and diagonal size. Enter horizontal resolution, vertical resolution, screen diagonal; the reported quantities are pixel density (PPI), approximate pixel pitch (mm/pixel). The equations and examples below show how those inputs lead to the result and where the model's assumptions matter.
Formula
PPI = sqrt(width² + height²) / diagonal inches
Worked example
With Horizontal resolution: 1920 pixels, Vertical resolution: 1080 pixels, Screen diagonal: 24 inches, pixel density is 91.787799 PPI.
Method and inputs
Treat the pixel grid as a rectangle. Use the Pythagorean theorem to calculate its diagonal pixel count, then divide by the measured screen diagonal in inches. Reciprocal density converted with 25.4 millimeters per inch gives approximate pixel pitch.
Worked example
A 1920 by 1080 display has a pixel diagonal of about 2,202.91 pixels. Across a 24-inch diagonal, that is about 91.79 pixels per inch and a pitch of roughly 0.277 millimeter per pixel.
A 1920-by-1080 panel at 27 inches has lower PPI than the same pixel grid at 24 inches because the pixels span a larger physical distance. The count of stored image pixels stays identical; only physical density changes.
How to read the result
PPI describes geometric pixel density, not image sharpness alone. Viewing distance, subpixel layout, scaling, contrast and rendering quality affect perceived detail. The pitch output gives the physical spacing implied by the geometry.
A 3840-by-2160 panel at the same 24-inch diagonal approximately doubles PPI and halves pixel pitch in each direction. Whether that is visible depends on viewing distance and eyesight, so PPI is a geometry measure rather than a universal quality score.
Assumptions and checks
The resolution should be the active pixel grid, and the diagonal should measure the actual viewable area rather than the outer case. Some displays have non-square pixels, for which the simple rectangular pixel geometry is imperfect.
Do not divide horizontal pixels by diagonal inches; include both width and height to form the pixel diagonal. Mixing centimeters with inches changes density by a factor of 2.54.
Common questions
What does the ppi calculator (pixels per inch) calculate?
It returns pixel density in pixels per inch and the associated approximate center-to-center pixel pitch.
When should I recalculate or check another method?
Recalculate for the actual viewable diagonal or a different resolution mode. If a device scales a lower-resolution image to the panel, native physical PPI remains unchanged although apparent image detail may not.
Inputs
- Horizontal resolution (pixels)
- Vertical resolution (pixels)
- Screen diagonal (inches)