Free Online Protractor & Photo Angle Finder
Measure angles on screen or photos online. Free 180° & 360° protractor, live camera overlay, roof pitch inclinometer, and 0.1° degree readout.
180° & 360° Protractor
Dual-scale inner & outer degrees, radians, and π fractions with a readout shown to the nearest 0.1°.
Measure on Photos & Images
Upload blueprints, diagrams, or pictures. Drag 3 coordinate points over any angle.
Camera & Gyro Inclinometer
Live AR camera guide lines and mobile tilt sensor to verify roof pitch and surface level.
How to Use an Online Protractor to Measure Angles
An online protractor is a virtual digital protractor that lets you measure an angle in a web browser instead of holding a physical tool against a worksheet or screen. This tool provides a readout shown to the nearest 0.1°, dual-scale guidance, radian and pi conversions, automatic angle classification, and 180°/360° measurement modes.
Select Protractor Span
Choose between a standard 180° semi-circle protractor for basic geometry, a 360° circular protractor for reflex angles, or a 90° right angle quadrant.
Align Baseline & Vertex
Position the central anchor circle at the vertex of the angle. Use the Base Rotation slider or quick rotation presets (0°, 90°, 180°, 270°) to match any tilted orientation.
Read Exact Angle & Type
Drag the red arm handle to intersect the target ray. The live dashboard instantly reports degrees (°), radians (rad), pi fractional notation (e.g. π/4), and angle classification.
Measuring Angles on Images, Diagrams, and Blueprints
Need to measure the slope of a roof from a photo, calculate the angle between clock hands, analyze orthopedic X-ray joint angles, or verify architectural blueprints? Our Image Protractor lets you upload any digital picture and overlay a fully movable, transparent 3-point angle finder:
- ✓ Upload Any Image: Drag and drop JPEG, PNG, WebP, or SVG files directly onto the workspace.
- ✓ Zero Server Uploads (100% Private): All image processing and angle mathematics are executed locally in your browser. Your images never leave your computer or phone.
- ✓ Interactive 3-Point Coordinate Ray Tracking: Drag the green vertex point, blue baseline ray, and red measurement ray across the image. Final accuracy depends on image quality, perspective, and handle placement.
Digital Angle Finder: Find Any Angle Online
Need an angle finder tool rather than a physical protractor? Place the center of the virtual protractor at the vertex, align the baseline with the first edge, and move the second arm to the other edge. The live readout shows the measured angle and classification. For photos and diagrams, use the image mode; for physical slopes, use the camera overlay or inclinometer.
Online Angle Finder
Measure an angle between two lines or rays directly in the browser.
Photo Angle Finder
Upload a picture, blueprint, or diagram and place the three measurement points over the angle.
Physical Slope Finder
Use device sensors or the camera overlay to align with a real-world slope, corner, or surface.
How to Measure Angles Without a Physical Protractor
For a worksheet, screenshot, photo, or on-screen diagram, you can measure an angle without carrying a plastic protractor. Use the interactive digital protractor for drawn geometry, or upload the image and position the measurement rays over the two sides of the angle. For a real object, switch to the camera overlay or device inclinometer when your phone supports the required sensor.
Types of Angles in Geometry: Definitions & Formulas
Angles are formed when two rays meet at a common endpoint called the vertex. Use this reference chart to identify and classify angles measured with the digital protractor:
| Angle Type | Degree Range | Radian Range | Geometric Definition | Real-World Example |
|---|---|---|---|---|
| Acute Angle | 0° < θ < 90° | 0 < θ < π/2 | An angle that is greater than 0° but strictly less than 90°. | Slice of pizza, open scissors (30°-60°) |
| Right Angle | θ = 90° | θ = π/2 | An angle of exactly 90 degrees, forming perpendicular lines. | Corner of a room, book edge, 3:00 on a clock |
| Obtuse Angle | 90° < θ < 180° | π/2 < θ < π | An angle greater than 90° but strictly less than a straight line (180°). | Reclined chair back, roof truss (120°-135°) |
| Straight Angle | θ = 180° | θ = π | An angle of exactly 180 degrees that forms a continuous straight line. | Flat horizon, 6:00 clock position |
| Reflex Angle | 180° < θ < 360° | π < θ < 2π | An angle that is greater than 180° but less than a complete revolution. | Outside bend of an open laptop (210°-300°) |
| Full / Perigon Angle | θ = 360° | θ = 2π | A complete 360-degree circular rotation bringing the ray back to start. | Complete wheel spin, 360° skateboard rotation |
180° vs 360° Online Protractor
Use the 180° protractor for standard school geometry and the 360° protractor when you need to inspect reflex angles or a full circular orientation. The interactive tool also offers a 90° quadrant for quick right-angle work.
180° Protractor
Best for acute, right, obtuse, and straight angles.
360° Protractor
Useful for reflex angles, rotations, and full-circle measurements.
90° Quadrant
A compact mode for checking right-angle relationships.
Online Protractor Practice for Geometry Students
Use the built-in online protractor practice quiz to test angle estimation, protractor reading, and angle classification. Each challenge gives you a target angle; submit your setting to see whether you matched it exactly or came within the practice tolerance, then continue your streak.
Roof Pitch Angle Reference & Digital Inclinometer
Roof pitch can be expressed as rise over 12 inches of run. The table below converts common pitch ratios into their approximate slope angles. For a physical roof, rafter, stair stringer, or ramp, the page's Gyro Inclinometer can read device tilt directly on compatible mobile hardware.
| Roof Pitch | Approx. Angle | Common Search Variant |
|---|---|---|
| 2/12 | 9.46° | 2/12 roof pitch angle |
| 3/12 | 14.04° | 3/12 roof pitch angle |
| 4/12 | 18.43° | 4/12 roof pitch angle |
| 5/12 | 22.62° | 5/12 roof pitch angle |
| 6/12 | 26.57° | 6/12 roof pitch angle |
| 8/12 | 33.69° | 8/12 roof pitch angle |
| 10/12 | 39.81° | 10/12 roof pitch angle |
Online Protractor Features at a Glance
Here is a quick overview of the practical measurement features available in this browser-based protractor:
| Key Feature | OneStepKit Online Protractor | Physical Plastic Protractor | Other Basic Online Tools |
|---|---|---|---|
| Angle Readout | 0.1° displayed resolution | Read from printed scale | Varies by tool |
| Measure on Photos / Images | ✓ Full Drag & Drop Image Tool | ✗ Impossible on screen | Limited / Clunky |
| Full 360° Circular Mode | ✓ 90°, 180°, and 360° Options | Requires separate 360° ruler | Fixed 180° or 360° only |
| Live Device Gyroscope | ✓ Mobile Orientation Tilt Sensor | ✗ None | ✗ None |
| Live Camera Transparent Mode | ✓ Real-time AR Camera Feed | ✗ None | ✗ None |
| Practice Angle Quiz Game | ✓ Built-in Quiz with Streaks | ✗ None | Basic or Separate app |
Using the Gyroscope Inclinometer for Slope & Level Verification
When working on carpentry, DIY woodworking, 3D printing alignment, pipe slope drainage, or framing, physical levels can be cumbersome. Our Gyro Inclinometer accesses your phone or tablet's internal orientation sensors (accelerometer & gyroscope) to measure:
Pitch Angle (Front-to-Back Tilt)
Measures vertical slope degrees when resting the long edge of your phone on stairs, wheelchair ramps, solar panel mounts, or roof rafters.
Roll Tilt & Surface Level Bubble
Provides a calibrated crosshair target bubble to check if table surfaces, picture frames, appliances, or shelving are perfectly level (0.0°).