What We Do

Screen Ruler Online provides a free, accurate on-screen measuring tool that works on any device with a web browser. Our ruler lets you measure real-world objects in centimeters, millimeters, and inches directly on your screen, without installing any software or downloading any apps.

The tool uses a calibration system based on physical reference objects (like a standard credit card) to determine your screen's exact pixel density. Once calibrated, measurements are accurate to within 0.5mm on most devices.

How It Works

Every screen has a unique pixel density measured in PPI (Pixels Per Inch). A 13-inch laptop screen and a 27-inch desktop monitor may share the same resolution, but their pixels are physically different sizes. Our calibration process measures this difference so the ruler can accurately convert screen pixels into real-world units.

We maintain a database of popular devices (iPhones, Samsung Galaxy phones, iPads, and more) with their known PPI values. When your device is recognized, we can provide instant measurements. For other devices, the credit card calibration method offers a reliable universal solution. You can read our full step-by-step guide for detailed instructions.

Who Uses Screen Ruler

Our users include designers verifying print dimensions, students measuring objects for homework, online shoppers checking product sizes, crafters cutting materials to size, and engineers doing quick physical measurements. The ruler is used in over 100 countries and serves people who need a quick, reliable measurement without reaching for a physical ruler or tape measure.

Supported Devices and Browsers

Screen Ruler Online works in Chrome, Safari, Firefox, Edge, and any modern browser that supports standard web technologies. It runs on iPhones, Android phones, iPads, Android tablets, MacBooks, Windows laptops, Chromebooks, and desktop monitors. No plugins, extensions, or special permissions are needed.

Our device database includes pre-configured PPI values for iPhone 12 through iPhone 15, Samsung Galaxy S23 and S24 series, iPad Pro, iPad Air, iPad mini, Xiaomi Redmi, Realme, OPPO, Vivo, and Samsung Galaxy A-series devices popular in India, Indonesia, and Turkey.

Supported Languages

Screen Ruler Online is available in 20 languages: English, Chinese (Simplified and Traditional), Spanish, French, German, Japanese, Korean, Hindi, Vietnamese, Thai, Turkish, Indonesian, Malay, Filipino, Czech, Romanian, Croatian, Serbian, and Sinhala. We continue to add new languages based on user demand.

Calibration Objects

The ruler supports calibration with multiple reference objects to serve users worldwide: credit cards (ISO standard), US quarters, US pennies, 1 Euro coins, UK pound coins, Indian Rupee coins (5 and 10 denominations), Indonesian Rupiah 1000 coins, Turkish Lira coins, and A4 paper. Visit our calibration objects page to see exact dimensions for each object.

Built by Developers, for Everyone

Screen Ruler Online was created by a team of web developers who needed a quick way to measure physical objects on screen during design reviews and hardware prototyping. After finding that existing solutions were either inaccurate, required downloads, or were cluttered with ads, we built a clean, calibration-based tool and made it free for everyone. The project is actively maintained and regularly updated with new device profiles, calibration objects, and language support.

Privacy & Data

Your calibration data is stored locally in your browser and is never sent to our servers. We use analytics to understand how people use the tool so we can improve it, but we do not collect any personal information. The ruler does not require an account, does not track individual users, and does not sell data to third parties. Read our full Privacy Policy for details.

Contact

Have a question, found a bug, or want to suggest a feature? We welcome your feedback. Leave us a message and we will get back to you.