Online Ruler

Measure in mm, cm, or inches — accurate to your screen

Select unit

mm (millimeters)cm (centimeters)inch

Measure distance

How it works

Select your preferred unit (mm, cm, or inches)
The ruler calibrates automatically using your screen's PPI
Click and drag across the ruler to measure
Results display instantly in your selected unit

Features

100% free — no signup or registration required
Works on all devices — desktop, mobile, tablet
Accurate measurements using screen PPI auto-detection
Multiple units: mm, cm, inches from a single codebase
Responsive design — works in any viewport

Frequently Asked Questions

Is this free?

Yes, this tool is completely free to use. No hidden fees.

Do I need an account?

No account or signup is required. The ruler works instantly.

How is it accurate?

The ruler auto-detects your screen's PPI (pixels per inch) by measuring a reference card width (85.6mm = standard credit card width). Calibration is stored locally in your browser.

Does it work on mobile?

Yes, this tool works on all devices including mobile phones and tablets. Touch supported.