Screen diagonal in pixels
sqrt(width^2 + height^2)
Screen scale tool
Screen PPI calculator for online ruler calibration
Calculate the CSS pixel density your browser uses for a screen. This gives a useful starting scale for an actual-size ruler, then you can confirm the result with a credit card or another known object.
Result
CSS pixels per inch
Enter a diagonal
CSS pixels per millimeter
-
Your browser screen size can be filled automatically. Enter the physical diagonal from your device specifications.
How the calculation works
Online rulers usually need CSS pixels per inch, not the raw hardware PPI printed in a device spec. Device pixel ratio and browser scaling can make those numbers different.
CSS pixels per inch
diagonal pixels / screen diagonal inches
CSS pixels per millimeter
pixels per inch / 25.4
When to use a PPI estimate
Estimating actual-size ruler scale from a monitor or laptop diagonal.
Checking whether browser CSS pixels differ from hardware pixel density.
Finding a starting calibration value before confirming with a credit card.
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Online ruler calibration guide
Use a credit card, screen diagonal, or known object to set the ruler scale.
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