Online Ruler

What it is

Online Ruler is a free web-based measurement tool that lets you measure distances on your screen with near pixel-perfect accuracy. After calibration, it achieves accuracy typically within 0.5mm for well-calibrated screens.

The tool offers three calibration methods: Auto-Detect (recognizes your device from a database of 100+ profiles), Screen Diagonal (enter your monitor's diagonal size in inches), and Credit Card Calibration (overlay a standard credit card for the most accurate results).

You can click any two points on the screen to measure distances horizontally, vertically, or diagonally. The ruler supports four measurement units: centimeters, millimeters, inches, and pixels. Place rulers on any edge of your screen—top, bottom, left, right, or any combination—and see real-time cursor coordinates as you move across the screen.

No installation or account is required. Online Ruler runs entirely in your web browser, saves your calibration locally on your device, and works on both desktop and mobile devices.

Questions from the bench

How accurate is the online ruler?

After proper calibration, the ruler achieves near pixel-perfect accuracy—typically within 0.5mm for well-calibrated screens. Accuracy depends on the calibration method: auto-detect works well for known devices, while credit card calibration provides the best accuracy for any screen.

What units can I measure in?

The ruler supports four measurement units: centimeters (cm), millimeters (mm), inches (in), and pixels (px). You can switch between units at any time.

Does it work on mobile devices?

Yes, the ruler works on tablets and mobile devices with touchscreen support. However, for the best experience and accuracy, using a laptop or desktop monitor is recommended since mobile screens are smaller and harder to calibrate precisely.

Is the ruler free to use?

Yes, Online Ruler is completely free with no ads, no account required, and no limitations.

Can I measure diagonal distances?

Yes, you can click two points anywhere on the screen to measure the distance between them—horizontally, vertically, or diagonally. The distance is displayed in your selected unit.