PPI Calculator from Inches and Resolution
PPI (pixels per inch) tells you how sharp a screen is. You only need two things: the screen's resolution (width × height in pixels) and itsdiagonal size in inches.
The formula
PPI = √(W² + H²) ÷ diagonal
First find the diagonal in pixels using the Pythagorean theorem (√(W² + H²)), then divide by the physical diagonal in inches.
Worked example
A 15.6-inch 1080p laptop (1920×1080):
√(1920² + 1080²) ÷ 15.6 = 141.2 PPI
Try it yourself
PPI Calculator
√(W²+H²) ÷ size — precise to 0.1 PPIUnit:
in
Use the diagonal printed on the box or spec sheet.
in wide
For when you measured the viewable width with a ruler.
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PPI
—PPI = √(W² + H²) ÷ diagonal · Retina-class estimate ≥ 300 PPI (approximate; depends on viewing distance)
Prefer working from physical width instead of diagonal? The calculator above also accepts width in inches.