Free online screen ruler in centimeters and inches. Calibrate to your display DPI for accurate real-world measurements. No downloads needed.
For accurate measurements, compare with a real object:
This free online ruler turns your screen into an accurate measuring tool. It uses your device's pixel density (DPI) to display real-world centimeter and inch scales. You can calibrate it against a known object like a credit card for even greater precision. All processing happens in your browser — no data is sent anywhere.
Accuracy depends on your screen's reported DPI and calibration. Most modern displays are accurate within 1-2% after calibration with a real object.
Yes, it works on any device with a screen. Mobile screens often have higher pixel density, so calibration is recommended for best results.
DPI (dots per inch) tells us how many pixels your screen packs into each physical inch. The ruler uses this value to convert pixels into real-world measurements.
Absolutely. All measurements and calibration happen entirely within your browser. Nothing is transmitted to any server.