How to Measure Angles Online
A practical walkthrough for measuring angles on photos, blueprints, worksheets, and live camera feeds with freeProtractor.
Step-by-Step Guide
Load your image or camera
Click Upload Image to open any picture, diagram, or homework screenshot (PNG, JPG, WEBP, SVG). You can also click Use Camera to measure an angle on a physical object directly through your webcam or phone camera, or simply use the blank canvas.
Choose your protractor mode (180° or 360°)
Use the standard 180° Semicircle for typical triangle geometry, acute, and obtuse angles. Switch to the 360° Full Circle protractor when you need to measure reflex angles (greater than 180°), circular pie charts, or compass bearings across all four quadrants.
Align the vertex and baseline
Drag the central crosshair handle directly onto the vertex (corner) of your angle. Then use the baseline rotation handle to line up the flat 0° reference line with the first arm of the angle.
Position the ray and read the measurement
Drag the ray handle along the scale until it lines up with the second side of the angle. The exact measurement updates in real time with degrees, radians, and trigonometric values (sin, cos, tan). Click anywhere along the arc to drop additional numbered pins if you are measuring multiple rays from the same vertex.
Log angles or export your work
Click Save Angle (or press the S key) to store the angle in your measurement table. When you are finished, you can export your log to CSV or download the marked-up canvas as an image for reports, assignments, or CAD references.
Helpful Tools & Shortcuts
Features designed to make measuring faster, clearer, and more accurate.
15° Magnetic Snap
Turn on Snap to magnetically latch onto milestone angles (0°, 30°, 45°, 60°, 90°, etc.) when your cursor gets close, making standard angle layouts effortless.
Keyboard Arrow Nudging
Use the ← / → arrow keys to nudge the active ray by 1.0°. Hold Shift + Arrow for ultra-precise 0.1° adjustments.
2.5x Precision Loupe
Enable Loupe to open a circular magnifying window over your cursor whenever you drag points, helping you target thin lines and distant vertices.
Centimeter & Inch Ruler
Toggle Ruler to overlay metric and imperial markings along the baseline ray, allowing you to check line lengths and angles in one view.
Complementary & Supplementary
Toggle Comp to shade complementary (90° − θ) and supplementary (180° − θ) sectors directly on the canvas for instant visual reference.
Auto-Save & Themes
Your pins, scale, position, and skin choice (Glass, Neon, Chalkboard, Solarized) save to your browser automatically, so your work is waiting even if you refresh.
Ready to measure an angle?
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