RULER°

Online Ruler

A free, accurate ruler for your screen. Supports centimetres and inches. Calibrate to your actual screen for precise measurements.

○ estimated
96 dpi
 

How to use the online ruler

  1. Select your unit — centimetres or inches — using the toggle above the ruler.
  2. Hover your cursor (or tap on mobile) over the ruler to measure.
  3. For accurate results, click Calibrate and use a credit card to match your screen's DPI.

Why calibrate your screen?

Every monitor has a different pixel density (DPI). Without calibration, the ruler uses a default of 96 DPI — fine for most screens, but off by up to 20% on high-density or retina displays. Calibrating takes 10 seconds and gives you measurements accurate to within 0.5 mm.

Frequently asked questions

Is this ruler accurate?
After calibration, yes. The ruler is accurate to within 0.5 mm on most screens. Without calibration it uses 96 DPI which is accurate on most standard monitors.
Does it work on mobile?
Yes. Tap and drag your finger along the ruler to measure. For best results on mobile, use the vertical ruler which spans the full height of your screen.

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