Online Actual Size Ruler

Calibrate your screen using a credit card
to measure real-world lengths.

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Actual Size Calibration

Accurately adjust with a card

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Multiple Units

Supports mm / cm / inch

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No Installation

Ready to use in browser

Screen Calibration

Please adjust using a physical object to ensure the ruler scale is accurate for your screen size.

TARGET

Move the slider below to make the frame on the screen exactly match the size of your physical credit card (or coin).

If your monitor is high resolution and you cannot match the physical size, please enter Fullscreen mode to calibrate.

Unit Converter

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Screen Resolution Tester

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Bazi Calculator

about,

About the Tool

The Online Ruler is a web-based tool that turns your device's screen into an actual size ruler. By calibrating the screen with a standard-sized object like a credit card or a local coin, it accurately displays measurements in millimeters, centimeters, and inches. It is perfect for situations where you need to measure small items but don't have a physical tape measure on hand.

how to,

How to Use

STEP 1

Select your calibration object (Credit Card, Coin, or Screen Diagonal) and move the slider until the on-screen frame matches your physical object.

STEP 2

Click 'Complete Calibration' to lock in the scale and reveal the actual size ruler on your screen.

STEP 3

Place the item you want to measure on the screen and drag the measurement box to see its exact length in your preferred unit (mm, cm, or inches).

glossary,

Glossary

Calibration: The process of adjusting the digital scale on your screen to match real-world physical dimensions.
DPI / PPI: Dots Per Inch / Pixels Per Inch. It represents the pixel density of your screen, which the tool calculates during the diagonal inch calibration method.
ID-1 Standard: An international standard (ISO/IEC 7810) that defines the size of bank cards (85.60 mm × 53.98 mm). Using an ID-1 card is the most globally reliable calibration method.

faq,

FAQ

Q. Is the online ruler completely accurate?: Once calibrated correctly with a standard object like a credit card (ID-1 size), it provides highly accurate measurements. However, please use it as a reference, as slight variations can occur based on screen viewing angles and browser zooming.
Q. Does this tool save any of my data?: No, this tool does not save any of your measurement data to our servers. Your calibration settings (px/mm ratio) are only saved locally in your browser's LocalStorage for your convenience during your next visit.
Q. What happens if I zoom in or out of the page?: Zooming in or out alters the scale of the browser. The tool automatically detects changes in zoom or device orientation and will display a warning prompting you to recalibrate to maintain measurement accuracy.