Online Protractor — Measure Angles on Screen (360° & 180°) | Cruse
Interactive online protractor to measure angles on screen. Features 180° and 360° modes, draggable angle indicator rays, and instant degree/radian readouts.
How to Use This Tool
Select Protractor Style
Switch between the standard 180° semicircle protractor or the full 360° circular protractor depending on your geometry problem or blueprint needs.
Position Vertex & Base Line
Drag the central orange vertex pin to the apex of the angle. Drag the blue baseline handle to align with the first ray or lock it horizontally to 0°.
Align Angle Pointer & Read Value
Drag the green target pointer handle along the arc. The exact angle updates in real-time in degrees (°), radians (rad), along with complementary and supplementary angles.
Optional: Upload Image to Measure
Click "Upload Image" to place a photo, blueprint, or diagram directly behind the transparent protractor to measure real angles without printing.
Technical Reference & Specifications
| Parameter / Standard | Specification |
|---|---|
| Protractor Geometries | 180° Semicircular & 360° Full Circular Navigation |
| Angular Precision | 0.1° resolution with sub-pixel pointer snapping |
| Units Displayed | Degrees (°), Radians (π rad), Gradians (grad) |
| Geometry Analysis | Angle classification (Acute, Right, Obtuse, Reflex), Complementary, Supplementary |
| Canvas Modes | Interactive Canvas with Draggable Vertex, Dual Pointer Rays, Image Overlay |
| Client Privacy | 100% In-Browser. No image data is ever sent to any server. |
Frequently Asked Questions
How do you measure an angle on screen with an online protractor?
Drag the central vertex pin of the protractor directly onto the corner (vertex) of the angle you want to measure. Align the baseline ray with one side of the angle, and drag the indicator pointer to the second side. The digital display immediately calculates the angle in degrees and radians.
Can I measure angles on an uploaded image or photo?
Yes! Click the "Upload Image" button in the toolbar. Select any JPG, PNG, or WebP diagram, textbook problem, or architectural plan. The image appears directly behind the protractor canvas so you can measure angles accurately on-screen.
What is the difference between a 180° and a 360° protractor?
A 180° protractor is a semi-circle ideal for measuring acute (under 90°), right (90°), and obtuse (90°-180°) angles. A 360° protractor is a complete circle capable of directly reading reflex angles (between 180° and 360°) and full rotations without manual subtraction.
How do I convert degrees to radians?
Degrees are converted to radians using the formula: Radians = Degrees × (π / 180). For example, 90° = 90 × (3.14159 / 180) = π/2 ≈ 1.5708 rad. This tool automatically calculates exact radian values in real time.
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