Free online ruler to measure 1 cm, inches, and any length on your screen. Calibrate to your display DPI for accurate real-world measurements. Perfect for quick online measurements without downloads.
For accurate measurements, compare with a real object:
This free online ruler turns your screen into an accurate measuring tool for quick 1 cm online measurements. It uses your device's pixel density (DPI) to display real-world centimeter and inch scales. Whether you need to measure 1 cm, check object sizes, or verify dimensions without a physical ruler, this tool provides instant results. 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.