Our Mission & Engineering
Accessible Geometry & Physical Measurement for Everyone
We believe that fundamental mathematical, drafting, and engineering instruments should be instantly accessible to every student, teacher, maker, and professional without paywalls, app installs, or privacy compromises.
0.1° High-DPI Precision
Engineered with sub-pixel 2.5x Loupe Magnifiers and floating-point trigonometry to ensure every degree, radian, and millimeter is calculated accurately.
100% Client-Side Privacy
Your photos, camera video streams, and sensor telemetry never leave your device. All calculations run strictly in your browser's local RAM.
100% Free Forever
No signups, no subscriptions, no locked features, and no intrusive watermarks on your exported PNG, SVG, CSV, or PDF worksheet diagrams.
The Comprehensive Measurement Suite
Virtual Protractor
180° Semicircle & 360° Full Circle angle protractor with ray snapping, lock, and export tools.
Screen Ruler (1:1)
Actual size physical ruler in cm, mm, in, and px with 59+ hardware device presets and ISO 7810 card calibration.
Image & Photo Protractor
Measure angles directly on photos, architectural blueprints, or clipboard screenshots (Ctrl+V) with 2-point scale calibration.
Live Camera AR
Real-world angle measurement using live webcam or phone camera feeds with gyroscopic gravity tilt-sync.
Compass & Inclinometer
360° Azimuth bearing navigation combined with dual-axis pitch/roll digital bubble spirit level.
Practice & Quiz
Gamified angle estimation and construction quiz with real-world engineering scenarios for students.
Editorial Board, Mathematical Accuracy & Testing Standards
Online Free Protractor is maintained by software engineers and mathematics educators dedicated to providing free, high-precision measurement tools. Every calculation is performed client-side using IEEE 754 double-precision floating-point arithmetic (Math.atan2, Math.hypot). Our calibration profiles are verified against real hardware across Apple, Samsung, Dell, Lenovo, and HP displays in controlled laboratory environments.
Have a Feature Suggestion or Question?
We actively listen to user feedback from classrooms, workshops, and engineering teams.
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