This online ruler works on any desktop or mobile screen. It automatically detects your device and scales the on‑screen ruler to real size. With full‑screen and calibration options, your tablet, phone, or computer becomes a true measuring tool no installation required.
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How to Use the Online Ruler
The ruler usually auto‑detects your device and displays accurate cm / inch scales. If detection fails, enter your screen size once or calibrate for pixel‑perfect dimensions.
1. 📱 Automatic Device Detection
Works out of the box—no setup.
- Recognizes 100 + Apple, Samsung, Google, and other devices.
- Applies the correct factory PPI.
- A green “Detected” box confirms accuracy.
- Settings persist between visits.
2. 💻 Set Your Screen's Diagonal
If auto‑detect fails, enter your screen’s diagonal or calibrate with a credit card. Your setting is saved for future visits.
Steps:
- Find the diagonal size (check device box or online search online model name).
- Enter it in Screen Diagonal.
- Click Apply.
3. 💳 Calibrate with a Credit Card
All bank cards share a standard width (85.60 mm/3.37 in) this allow calibrate accurate size for the ruler.
Steps:
- Calibrate > Open Credit Card calibration.
- Place a card on the blue guide.
- Adjust the slider until the guide matches the card.
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Supported Devices and Browsers
Our online ruler works on all modern devices and browsers with automatic detection for 100+ device configurations.
Automatically Detected Devices
- Apple: iPhone, iPad, MacBook, iMac, Studio Display
- Samsung: Galaxy S series, Note series, Fold/Flip devices
- Google: Pixel phones and tablets
- Windows: Surface devices, popular laptop configurations
- Monitors: Common desktop monitor sizes and resolutions
Browser Compatibility
Works perfectly on:
- Chrome (desktop and mobile)
- Safari (iOS and macOS)
- Firefox (all platforms)
- Edge (Windows)
- Opera (all platforms)
If your device isn’t detected, use quick calibration or manual entry for accuracy.
verified Tips for Best Results
- Keep browser zoom at 100 %.
- Re‑calibrate when switching devices or monitors.
- JavaScript is enabled