Browser-based angle measurement tool
Measure angles online.
Upload a diagram, paste a screenshot, or start with the drafting grid. Drag the vertex and arms to measure any angle live. Calibrate your screen for real-world scale. Fully offline — nothing leaves your browser.
Drag & Drop or Paste an Image
Paste directly using Ctrl+V / Cmd+V, drop a file, or click 'Upload Image' above. Measuring works immediately!
Geometry & Education Mode
Angle Classification
An angle is formed when two straight lines or rays meet at a shared endpoint called the **vertex**. Here, the protractor center is placed on the vertex to measure the angular rotation from the base line.
Related Trigonometry
Trigonometry outputs are computed relative to the base line. Complementary angles sum up to 90°, and supplementary sum up to 180°.
Live Measured Angle
Screen Calibration96 DPI
We query your system's hardware configurations and device pixel ratios to auto-estimate screen size.
Enter your screen's physical diagonal size in inches to calculate exact pixels-per-inch (PPI).
Formula: DPI = √(width² + height²) / diagonal
Hold a physical credit card against your screen and adjust the slider until the on-screen card matches the physical card.
Standard card size: 3.37 inches (85.6mm) wide.
Protractor Options
Load Demo Worksheet
Measurement History
No saved measurements yet.
Geometry Calculators
Solve triangle dimensions based on the active measured angle $\theta$.
How to measure angles using an online protractor.
An **online protractor** is a digital instrument designed to measure angles directly in your web browser. Unlike a physical tool made of plastic or metal, a virtual protractor works dynamically on images, PDF diagrams, architectural drawings, or geometric shapes.
Set your Vertex
Align the central origin target of the protractor (the vertex) directly over the corner or intersection where your two lines meet. Drag the center crosshair handle to position it.
Align the Baseline
Drag the **Base Arm (A)** along the first line of your angle. The protractor circle automatically rotates and locks its zero-degree mark ($0^\circ$) to this starting direction.
Measure the Angle
Drag the **Measuring Arm (B)** along the second line. The live angle displays instantly in degrees and radians in the dashboard, alongside slope pitch and trigonometry.
Key features of this tool
Frequently Asked Questions
How do I paste an image directly from my clipboard?
Simply select this browser page tab, copy any image screenshot (using e.g. Snipping tool or print-screen) to your clipboard, and press **Ctrl + V** (or **Cmd + V** on Mac). The image will load instantly.
Why calibrate with a credit card?
Every screen has a different physical density (DPI). By adjusting the on-screen box to match a standard physical object like a credit card (which is exactly 3.37 inches wide), we establish an exact pixels-per-inch scale factor.
Can I measure complementary and supplementary angles?
Yes. The control panel automatically displays supplementary angles ($180^\circ - \theta$) and complementary angles ($90^\circ - \theta$) in real-time, making it useful for geometry homework and engineering reports.
Does this online protractor support 360 degrees?
Yes. You can toggle between 180° (semicircle) and 360° (full circle) mode inside the **Protractor Options** menu in the sidebar.
A browser-based protractor for measuring angles on images and diagrams
This tool lets you measure angles directly in your browser by overlaying a draggable protractor on any image. Upload a photo, paste a screenshot, or use the built-in drafting grid, then position the vertex and arms to read any angle in real time. It works offline — no data is sent to a server.
Why use a browser-based angle measurement tool?
Physical protractors only work on paper, and many online alternatives are cluttered with ads or require you to sign up. This tool runs entirely in your browser with no accounts, no ads, and no uploads to external servers. It supports 180° and 360° modes, multiple simultaneous angle measurements, and screen calibration so you can convert pixels to real-world units.
Real-time angle display
The tool shows the measured angle in degrees and radians as you drag the arms. It also computes complementary and supplementary angles, slope pitch, and basic trigonometry values — useful for geometry, drafting, and engineering work.
Works on top of any image
The protractor overlays your loaded image, so you can measure angles on photographs, scanned documents, blueprints, or screenshots. Drag the vertex to the corner you want to measure, align the base arm, then move the measuring arm to read the angle.
For students and educators
The built-in Geometry & Education mode classifies angles (acute, right, obtuse, straight, reflex) and shows their ranges. Students can upload geometry worksheets and practice measuring angles, or use the trigonometry panel to see sin, cos, and tan values update live. It works on tablets and laptops, making it suitable for classroom or remote learning.
Teachers can project the tool during lessons to demonstrate angle concepts, and students can independently practice by loading diagrams and measuring angles on their own devices.
Advanced features
How to use this tool
Getting started takes three steps:
Load an image
Upload a file, paste a screenshot from your clipboard (Ctrl+V / Cmd+V), drag and drop an image, or start with the built-in drafting blueprint.
Position the protractor
Drag the vertex crosshair to the corner you want to measure. Align the base arm (A) along the first line. Use arrow keys and bracket keys for fine adjustment.
Read the angle
Drag the measuring arm (B) to the second line. The angle appears instantly in the live display panel, with complementary, supplementary, and trigonometry values.
Who uses this tool?
A wide range of people use this tool for angle measurement tasks:
- Students & Teachers: For geometry lessons, homework, and classroom demonstrations of angle concepts
- Engineers & Architects: To measure angles on blueprints, floor plans, and technical drawings
- Woodworkers & Craftsmen: For verifying cut angles on photos of joinery and furniture
- Photographers: To analyze composition angles and perspective lines in images
- DIY Enthusiasts: Quick angle checks for home improvement and renovation projects
Start measuring angles now
Open the tool, load an image, and begin measuring. Works on desktop, tablet, and mobile. No registration required, no data collected, and everything runs locally in your browser.
Try the protractor