True Size Ruler

True Size Ruler is a free online ruler that displays measurements at their actual physical size on any screen — no printing or downloads required. Simply open the page, calibrate to your display in seconds, and measure anything in centimeters, millimeters, or inches with real-world accuracy.

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About — Accurate online screen ruler. True Size auto-detects PPI for pixel-perfect measurements in cm, mm, and inches. Calibrate instantly on any digital display.
Contact — Questions, feedback, or bug reports — we'd love to hear from you.
How It Works — True Size screen ruler calculates true PPI using auto-device detection, diagonal formulas, or physical credit card calibration for precise accuracy.
Privacy Policy — True Size privacy policy: We collect no personal data or tracking cookies. All ruler calibration runs locally in your browser.
Blog — Guides, explainers, and reference articles about screen measurement, display technology, and precision tools.
FAQ Page — Everything you need to know about True Size Ruler.
Terms Of Service — True Size Terms of Service: Free on-screen ruler provided "as is." Read our accuracy disclaimer, intellectual property rules, and limitation of liability.