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Free On-Screen Ruler โ€” Measure in cm, mm & Inches

Place an object against your screen to measure it. Calibrate first for accurate results.

Calibrate for Accuracy

Hold a credit card (85.6mm) against the ruler and adjust PPI until it matches.

Browser reports device pixel ratio: โ†’ estimated PPI:

Measurement

0.00 cm

Click and drag on the ruler to measure a length

How to Use

  1. Calibrate โ€” Turn on Auto-detect or manually adjust PPI. Verify with a credit card (85.6mm / 3.37").
  2. Choose unit โ€” CM, MM, or Inches.
  3. Choose orientation โ€” Horizontal or Vertical.
  4. Measure โ€” Click and drag along the ruler, or place an object against the screen.
  5. Pick Up โ€” Click "Pick Up" to make the ruler moveable. Drag it anywhere on screen and click "Drop" to anchor it.

About Auto-detect

The browser reports your device's pixel ratio (DPR). We multiply your screen's CSS pixel resolution by DPR to estimate physical PPI. This is a good starting point but may not be exact โ€” a credit card test gives the best calibration.

Report a bug | Suggest a new feature for this tool โ†’