Online Screen Ruler – Calibrated Millimeter & Inch Ruler

How to Use the On-Screen Ruler

1. Calibrate First: If you have not calibrated yet, click "Calibrate" and place an ATM, credit, or debit card over the screen. Align the card edge to the outline to configure exact pixel scaling.
2. Place the Object: Place your coin, key, screw, or card flat against the device display. Align one edge with the zero mark (or left jaw).
3. Drag the Measurement Jaws: Touch or click-and-drag the orange pointer to span the object's width. The readout displays the exact measurement instantly.
4. Switch Units: Toggle between mm (millimeters), cm (centimeters), in (inches), and traditional gaj (yards).

Accuracy and Optical Precautions

Screen rulers are accurate to approximately ±0.5 mm when calibrated correctly. Keep in mind:

• Protective Glass: Thick screen protectors introduce a small optical gap (parallax). Always view straight from above.
• Browser Zoom: Keep your browser zoom at 100%. If you pinch-zoom or adjust browser scale, press "Calibrate" to reset the scaling factor.
• For in-depth details on pixel density and accuracy boundaries, read our Screen Ruler Calibration Guide.