Ruler Online - Free Digital Measuring Tool

Accurate online ruler with auto calibration, supports cm and inches

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How to Use the Online Ruler

đź“Ś Accuracy Tips: For best measurement accuracy, please ensure:
1. Your browser is set to 100% zoom (no zoom in or out).
2. Your screen size (in inches) is correctly detected or manually set.

Confirm Your Screen Size

The app tries to auto-detect your screen size. For more precise results, you can manually enter your screen’s diagonal size in inches (e.g. 13.3", 15.6"). This ensures ruler accuracy.

Keep Zoom at 100%

Make sure your browser zoom is set to 100%. Zooming in or out will distort the on-screen scale and lead to incorrect measurements.

Choose Your Units

Easily switch between centimeters and inches, depending on what you’re measuring or your personal preference.

Start Measuring

Place any object directly on your screen and read the values instantly. Perfect for measuring cards, jewelry, or small tools.

Works on All Devices

Our ruler tool works on desktops, laptops, tablets, and more. Just make sure your screen size is confirmed for best results—no installation needed!

About Ruler Online

Ruler Online is a smart, high-precision digital ruler that instantly turns your screen into a real-world measuring tool.
With automatic screen size detection and intelligent calibration, it delivers accurate results with zero effort. Simply confirm your screen size—and start measuring with confidence.

Key Features

    Measure in centimeters or inches instantly
    Auto-detects and adjusts to your screen size for optimal accuracy
    Minimalist, distraction-free interface for a smooth measuring experience
    Fully compatible with all desktop, laptop, and monitor screens
    No downloads or extensions required—just open and use

How It Works

Ruler Online analyzes your screen’s physical dimensions and resolution to calculate its DPI (dots per inch). This allows accurate pixel-to-real-world unit conversion—ensuring that the ruler you see on screen reflects actual size.

Accuracy Reminder

To ensure precise measurements:
âś… Keep your browser zoom at 100% (avoid zooming in or out)
âś… Confirm or manually set your screen's diagonal size (e.g. 13.3", 15.6", etc.)

Use Cases

Whether you're measuring small items, checking product dimensions, working on designs, or just need a ruler in a pinch—Ruler Online is your go-to tool.
No tools? No problem. It’s ready to help anytime, anywhere.