Last updated: March 2026
What Is the Screen Ruler?
The Screen Ruler is a free online measuring tool that displays a real-size ruler on your screen. Measure physical objects by holding them up to your display, or measure on-screen elements with pixel-perfect precision.
After a quick one-time calibration using a credit card or coin, the ruler shows accurate measurements in both inches and centimeters. It works on any screen size — monitors, laptops, tablets, and phones.
No app to download, no signup needed. Open the page, calibrate once, and start measuring immediately.
Key Features
Dual units. Displays inches and centimeters simultaneously with fine subdivisions — 1/16 inch and 1mm markings for precise measurements.
Easy calibration. Match the ruler to a credit card, coin, or known-size object. One calibration and you're set for accurate measurements on your specific screen.
Works on any device. Responsive design adapts to monitors, laptops, tablets, and phones. The ruler scales correctly after calibration regardless of screen size or resolution.
No installation required. Runs entirely in your browser. Bookmark it for instant access whenever you need a quick measurement.
Frequently Asked Questions
How accurate is the screen ruler?
The ruler is highly accurate after calibration. Use the calibration tool to match a known object (like a credit card or coin) to set your screen's DPI correctly. Once calibrated, measurements are accurate to within 1mm.
How do I calibrate the ruler for my screen?
Hold a credit card, coin, or other object of known size against your screen. Adjust the calibration slider until the ruler markings match the object's actual size. This compensates for different screen sizes and resolutions.
Can I measure objects in both inches and centimeters?
Yes. The ruler displays both inches and centimeters simultaneously. You can switch between metric and imperial as your primary unit. Markings show subdivisions down to 1/16 inch and 1mm.
Does the screen ruler work on mobile phones?
Yes. The ruler is fully responsive and works on phones and tablets. Calibrate it for your specific device for the most accurate measurements. Touch and drag to position the ruler on screen.