Welcome to the most accurate free digital protractor accessible directly in your web browser. Designed for architects, engineers, woodworkers, students, and graphic designers, this precision on-screen angle gauge allows instantaneous measurement of physical objects and digital graphics. Supporting both classic 180° semicircle and full 360° circle modes, the protractor displays live readouts in degrees (°), radians (rad), gradient slope (%), and supplementary angles with 0.1° accuracy.
Traditional plastic protractors can easily smudge pencil lines or be misplaced. Our digital protractor turns your laptop, tablet, or smartphone screen into a contact-grade drafting workbench. Here is how to measure any physical or on-screen angle in three easy steps:
Different engineering and scientific disciplines demand different representations of angular geometry. True Scale Protractor calculates multiple mathematical units simultaneously:
rad = θ × (π / 180)).tan(θ) × 100%, essential for roof pitches, civil engineering gradients, and ramp design.180° - θ), allowing immediate calculation of adjacent corners without manual mental arithmetic.Switch effortlessly between two specialized protractor layouts to suit your specific measurement project:
Whether verifying miter saw blade bevels, inspecting 3D printed mechanical joints, measuring fabric patterns, or checking rotational angles in presentation software like PowerPoint Online or Google Slides, our digital protractor delivers instant contact verification with zero downloads and 100% offline Progressive Web App support.
Everything you need to know about measuring angles and using our online digital protractor.
To measure an angle on screen, place your physical object or align your digital artwork directly against the display. Position the protractor vertex (center point) at the intersection of the two lines, and align the baseline ray with the horizontal edge. Then drag the circular angle handle along the arc until the pointer aligns flush with the second edge. The live readout badge displays the exact angle in degrees, radians, and slope percentage.
Yes! True Scale Protractor works seamlessly on iPhone, iPad, and Android mobile touchscreens. You can safely place small parts, carpentry wedges, architectural drawings, or craft templates directly against your mobile screen. Use the Lock feature to freeze the canvas so touch contact does not cause accidental viewport panning.
The 180° Semicircle mode is the standard classroom and drafting layout, ideal for measuring acute, right, and obtuse angles up to 180 degrees. The 360° Full Circle mode provides a complete circular azimuth scale, perfect for reflex angles (>180°), circular rotation, compass headings, robotics joints, and polar coordinate verification.
Our live readout automatically converts degrees into radians and pitch slope. Radians are calculated using Radians = Degrees × (π / 180), while slope percentage is computed using Slope = tan(Angle) × 100%. For example, a 45° angle equals 0.79 radians and a 100% slope gradient (1:1 rise over run).
When creating presentation graphics, charts, or diagram callouts in PowerPoint Online, open True Scale Protractor in a side-by-side or layered browser window. Use our angle presets (0°, 45°, 90°, 180°) or customize the protractor angle to visually verify rotation angles, diagonal banners, and geometric alignment before finalizing slides.
Because angles represent rotational ratios rather than linear distances, relative angular degrees remain mathematically sound even on uncalibrated screens. However, calibrating your screen ensures that the physical dimensions of the protractor radius and tick marks match standard physical drafting instruments at true 1:1 scale.