Online Ruler

Free online ruler in inches and online ruler in cm. Calibrate with a credit card or set custom PPI for accurate measurement on any screen. View both centimeters and inches with horizontal or vertical orientation.

Current PPI: 96
Screen Resolution:
Ruler Length: Calculating...
Scales: ● Centimeters (bottom) | ● Inches (top)

How to Use the Online Ruler

  1. Calibrate Your Screen: Use the Credit Card Calibration button for the most accurate PPI. Adjust the red line to match the card’s width, then click Apply.
  2. Or Set PPI Manually: Enter your Custom PPI or calculate it from your screen diagonal.
  3. Choose Orientation:
    • Horizontal: Inches on top, centimeters at bottom.
    • Vertical: Same scales along the side.
  4. Read the Measurements:
    • Centimeters: Numbers appear at the bottom; millimeter marks help precise measurement.
    • Inches: Numbers at the top; fractional marks show ¼, ½, ¾ inches.
  5. Tips: Resize your browser if needed; the ruler adapts automatically. Recalibrate if switching monitors or resolutions.