Calculate screen PPI and aspect ratio

Derive total pixels, reduced aspect ratio, pixels per inch, and the distance where one pixel spans one arcminute.

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ToolScreen Resolution Calculator
Input
Output
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Preview

How it works

Pixel density is √(width² + height²) divided by physical diagonal inches, while the greatest common divisor reduces pixel width and height to an aspect ratio. One-pixel pitch divided by tan(1 arcminute) gives the corresponding distance; that angle is the conventional 20/20 detail threshold, not a comfort recommendation.

Formula
PPI = √(width pixels² + height pixels²) ÷ diagonal inches
  • Pixel dimensions and physical diagonal are all required because a “1080p” or “4K” label alone does not determine density.
  • No observer acuity, operating-system scaling, contrast, or ergonomic preference is assumed.

Worked example

A 24 inch 1080p monitor
Input
											Width px: 1920
Height px: 1080
Diagonal inches: 24
Output
												Total pixels: 2073600
Aspect ratio: 16:9
PPI: 91.79
One arcminute distance inches: 37.45
One arcminute distance cm: 95.13

When to use this

Monitor comparisons distinguish same-resolution panel sizes, UI asset checks compare source pixels with panel density, and display planning compares desktop, television, and projection pixel pitch.

Edge cases

  • A 24-inch value must be the panel’s corner-to-corner diagonal, not its physical width; using width overstates PPI.
  • 3840×2160 reduces to 16:9 regardless of the “4K” marketing label because the ratio comes from the actual pixel dimensions.
  • One arcminute is a conventional 20/20 resolution threshold, but acuity, contrast, scaling, content, and comfort vary, so the distance is not ergonomic advice.

References