Calibrate the Online Ruler to Your Screen

Set the relationship between browser pixels and physical size on the display you are using. Choose the reference method you can verify most confidently.

Credit card reference

Place a standard bank card over the guide and adjust the width.

85.60 mm

Screen diagonal

Enter the manufacturer’s physical diagonal for the active screen.

Bank-card calibration

A standard ID-1 bank card is 85.60 mm wide. Hold the card flat against the screen and adjust the guide until its width matches the physical card, then save the value. This gives the current display a direct real-world reference.

Screen-diagonal calibration

If you know the physical diagonal of the active display, enter it in inches. 1Ruler combines that number with the screen dimensions reported by the browser to calculate the working scale.

When to recalibrate

  • After moving the browser to another monitor.
  • After changing browser zoom or operating-system display scaling.
  • After switching between mirrored and extended displays if the active screen changes.
  • Whenever a known object no longer matches the ruler.

Calibration is stored locally

The saved value stays in your browser so you do not need to repeat the same setup on every visit. Clear the calibration at any time from the calibration controls.