📐 Virtual Protractor
Measure angles precisely — degrees, radians, gradians.
Online Protractor — Measure Angles Online, Instantly
No physical protractor? No problem. This free virtual protractor lets you measure, set, and save angles directly in your browser in degrees, radians, or gradians with zero downloads and zero fuss.
What is a Online Protractor?
A virtual protractor is a browser-based angle measurement tool that replicates what a physical semicircular protractor does only better. Instead of squinting at printed degree markings and hoping your pencil line stays straight, you place points on a digital canvas and get an exact reading down to two decimal places.
This tool goes beyond a basic protractor image. It gives you live angle values in three unit systems simultaneously, interactive arm-dragging, image upload for real-world measurement, and a save-angle feature so you can track multiple readings without jotting anything down on paper.
Key features at a glance
Three unit systems
Read your angle in degrees, radians, and gradians — all updated live as you drag.
2-line and 3-point modes
Drag two arms from a vertex, or click three points to define an angle from any shape or image.
Image upload
Drop a photo or screenshot onto the canvas and measure angles directly on your image.
Save angles
Bookmark specific readings during a session. Useful when comparing multiple measurements.
Snap to 5°
Enable snapping for quick exact angles great for setting 30°, 45°, 60°, or 90° in one click.
Trig values live
See sin, cos, and tan update in real time no need to reach for a calculator.
How to use the online protractor — step by step
The tool is designed to be picked up without reading a manual, but here is exactly what each step looks like so you can get accurate results on your first try.
2-line mode (default)
- Click the canvas to place the vertex — the point where your two angle arms meet.
- Drag the first arm outward in any direction. The angle readout starts updating immediately.
- Drag the second arm to set the opening of the angle you want to measure or display.
- Read the angle in the panel on the right — degrees, radians, and gradians all shown at once.
- Optional: hit Save Angle to bookmark this reading, then reposition the arms for your next measurement.
3-point mode (best for images)
- Switch to 3-Point in the mode selector at the top.
- Upload your image using the image upload button — a photo, diagram, or screenshot.
- Click three points on the image: the first ray endpoint, the vertex (corner), and the second ray endpoint.
- The tool calculates the exact angle formed by those three points and displays it instantly.
Tip: Use the Snap to 5° toggle when you need a clean standard angle (45°, 90°, 120°, etc.) and do not need decimal precision. Turn it off when measuring angles from real images where exact decimal values matter.
Slider mode
Slider mode lets you dial in a specific angle value numerically rather than dragging arms. Type or scrub to any degree value and the protractor arms reposition to match. Handy for students checking whether a drawn angle is correct, or for teachers demonstrating specific angle types in class.
Understanding the three angle units
The panel always shows all three units side by side so you never need to convert manually.
°
Degrees
0 – 360
rad
Radians
0 – 2π
grad
Gradians
0 – 400
Degrees are what most people know from school a full circle is 360°. Radians are used in mathematics, physics, and programming; a full circle is 2π (roughly 6.283). Gradians divide a right angle into 100 equal parts, making a full circle 400 grad a system used in surveying and some European engineering workflows.
Angle types explained
The info panel identifies your angle type automatically. Here is what each label means:
| Type | Range | Common uses |
|---|---|---|
| Zero | 0° | Reference baseline, no opening between arms |
| Acute | 0° – 90° | Sharp corners, roof pitches, triangle interiors |
| Right | exactly 90° | Carpentry, engineering, perpendicular lines |
| Obtuse | 90° – 180° | Wide corners, polygon interior angles |
| Straight | exactly 180° | Flat lines, supplementary angle pairs |
| Reflex | 180° – 360° | Gear teeth, cam profiles, rotation tracking |
| Full | exactly 360° | Complete rotation reference |
Online protractor vs physical protractor — honest comparison
| Feature | This tool | Physical protractor |
|---|---|---|
| Precision | ✓ Two decimal places | ±0.5° at best |
| Unit conversion | ✓ Instant, automatic | ✗ Manual calculation |
| Measure from images | ✓ Upload & click | ✗ Not possible |
| Trig values | ✓ Live sin/cos/tan | ✗ Need separate table |
| Save readings | ✓ Session bookmarks | ✗ Must write down |
| Works on mobile | ✓ Touch-friendly | ✓ Yes |
| Cost | ✓ Free | Small cost |
| No download needed | ✓ Browser only | ✓ Physical object |
Physical protractors are still useful when you need to mark an angle directly on paper or material. For everything else reading, checking, converting, and recording angles the virtual version wins on every metric that matters.
Who uses a Online Protractor?
The use cases are broader than you might expect:
- Students and teachers geometry homework, classroom demonstrations, checking drawn angles without buying class sets of protractors.
- Architects and engineers quick angle checks from scanned drawings or photos without opening CAD software.
- Woodworkers and DIY builders measure a bevel or miter from a photo before setting a saw blade.
- Photographers and designers check the horizon tilt of a photo or the rotation of a design element.
- Programmers verify radian values when working on graphics, game physics, or animation curves.
- Surveyors gradians output is directly useful without conversion in many field calculations.
Display options and power features
Most users never need to touch the display options, but they exist for a reason:
Arc radius adjusts how large the arc indicator drawn between the two arms appears. Smaller arcs keep the canvas cleaner when you are working with multiple saved angles. Larger arcs are clearer for presentations or screenshots.
Show grid adds a background grid to the canvas useful when you want a visual reference for horizontal and vertical alignment.
Bisector line draws the angle bisector the ray that splits your angle exactly in half. This is genuinely useful for geometry work and for setting up symmetrical cuts in woodworking or metalwork.
Compass rose overlays a directional compass on the canvas. Useful when working with bearings rather than standard mathematical angles.
Complement, supplement, and reflex what the panel shows
Beyond the raw angle value, the information panel automatically calculates related angles:
- Complement: The angle that, when added to your current angle, makes 90°. Only shown when your angle is less than 90°.
- Supplement: The angle that adds to yours to reach 180°. Only shown for angles under 180°.
- Reflex: The angle on the other side — 360° minus your current reading. Always shown.
- These automatic calculations save time during geometry work where you constantly need related angle values.
Quick-set angles
The quick-set buttons at the bottom of the panel (0°, 30°, 45°, 60°, 90°, 120°, 135°, 150°, 180°, 270°, 360°) are shortcuts that snap both arms to a precise standard angle in one click. These are the angles that come up most often in geometry, construction, and design work. Instead of carefully dragging to hit exactly 45° by hand, one click gets you there.
Frequently Asked Questions
Yes, completely free. No account, no download, no time limit. Open the page and start measuring.
The angle calculation is based on arc tangent math applied to pixel coordinates, giving precision to two decimal places. The limiting factor is how accurately you place your click points — for image measurements, zooming in on the target area before clicking gives tighter results.
Yes. Use the image upload button to load any image onto the canvas, then switch to 3-point mode and click the three points that define your angle. This is the most popular use case for the tool.
Yes. The canvas responds to touch events so you can drag arms and place points with your finger on any touchscreen device.
In 2-line mode you drag two arms from a central vertex best for setting or demonstrating a specific angle. In 3-point mode you click three coordinates and the tool calculates the angle between them best for measuring angles that already exist in an image or drawing.
You do not need to the tool shows both simultaneously. If you need the formula: radians = degrees × (π / 180). For example, 90° = 90 × 0.01745 = 1.5708 rad.
Yes. The gradian readout is live and precise. A right angle reads as exactly 100 grad, which matches the gradian system used in European surveying and some navigation workflows.