Online protractor

Everything runs locally in your browser. A photo you choose is drawn on screen and never uploaded anywhere; close the tab and it is gone.

The placement rules are the same as on paper — origin on the vertex, baseline on one ray, read the scale that starts at 0° on that ray. If that is new to you, start with How to use a protractor, the step-by-step guide with diagrams. Need a physical one? Print a real-size printable protractor (180° and 360°).

What you can do with it

• Measure an angle on screen. Line the baseline up with one edge of anything on your display and swing the arm to the other — a diagram, a PDF, a screenshot.
• Draw an exact angle. Type 37 and the arm sits at 37°. Hold paper against a tablet to trace it, or use it as an angle maker to show what each angle looks like.
• Measure an angle in a photo. Load a picture of a roof, a corner, a bike frame, a golf swing — put the vertex on the corner, the two arms on the edges, read the angle. The step-by-step is in how to measure an angle in a photo.
• Full-circle protractor. 360° mode handles reflex angles and full turns.
• Practice reading angles. Guess the target, check, improve — useful before a geometry test.
• Touch, mouse, or keyboard. Arrow keys nudge by 1°, Shift + arrow by 10°.

When a screen protractor is enough — and when it isn't

An online protractor is perfect for measuring an angle in an image, teaching how angles work, or a quick sanity check. What it can't do is measure a real object: you can't lay your monitor against a table leg or a roof. That's the gap the Protractor app fills — rest your iPhone on the surface and it reads the angle from the same sensors behind Apple's level, in degrees, percent slope, or an X-in-12 ratio. For the underlying method, see how to measure an angle and how to use a protractor.

An online protractor for students and teachers

A virtual protractor is a clean way to learn how angles work. There's no parallax error from reading a printed scale at an angle, the value updates as you drag, and it's the same on every device — useful for classrooms, homework, and quick practice. Project it on a whiteboard to demonstrate acute versus obtuse angles, let students check an answer, or run the practice mode as a two-minute warm-up. The names of each range are in types of angles; drawing on paper is in how to draw an angle with a protractor.

For many more free virtual manipulatives, from fractions to geometry, Virtual Manipulatives on the Web by Dr. Patricia Deubel at CT4ME is a long-running, well-organized directory for teachers.

When you're ready to measure angles out in the world, see angle measuring tools and the angle finder page — which also has a sensor-based angle finder that runs in your phone's browser.

For angles you meet as a slope rather than a drawing, two other tools on this site do the conversion for you: the roof pitch calculator turns a rise-over-run pitch into degrees (and back), and the digital level reads the tilt of a real surface straight from your phone's sensors.