About Online Ruler
Crafted to deliver instant, clutter-free physical scale measurement on any screen bezel.
Why We Built Online Ruler
Traditional online rulers are often plagued by invasive ads, confusing menus, inaccurate default PPI values, and clunky popups. When you need to measure a bolt, check paper dimensions, or size an envelope, you want immediate access to a calibrated scale without friction.
Online Ruler was developed as a clean, fast, and privacy-conscious web instrument that turns your smartphone, tablet, or monitor bezels into a precision physical ruler.
How Our Accuracy Works
Digital screens do not inherently report their physical pixel density to browsers for privacy and fingerprinting reasons. To achieve true 1:1 real-world scale, Online Ruler implements a 3-tier calibration engine:
Calibrate using any standard credit card, ID card, or gift card (precisely 85.60 mm × 53.98 mm under ISO/IEC 7810 ID-1).
Instant detection database matching popular MacBooks, iPhones, iPads, and common desktop displays based on viewport and devicePixelRatio.
Mathematical PPI calculation derived from your screen's known diagonal size in inches using Pythagoras' theorem.
Zero Data Tracking, Pure Utility
We believe utility web tools should respect user privacy. All your calibration points, unit selections, and custom shortcuts are persisted strictly on your own device through browser local storage. No trackers, no accounts, and no downloads required.