Measure and construct angles with a virtual protractor. Convert between degrees, radians, and gradians with visual arcs.
This tool overlays a virtual protractor with two draggable rays so you can read an angle directly, or you can type a value into a numeric field and get it converted across degrees, radians, and gradians at once. The arc redraws live as you drag, showing the swept angle at the vertex. The most common surprise is the gradian column: it looks like a typo of degrees to anyone who has not used surveying units, since 90 degrees becomes 100 gradians, not 90.something.
A concrete input and expected output from the current implementation.
Input
45
Expected output
45 deg = 0.7854 rad = 50 grad
45 x (pi/180) = 0.785398... radians, and 45 x (400/360) = 50 gradians, since a full turn is 360 degrees, 2*pi radians, and 400 gradians.
Two rays share a common vertex; dragging either one recalculates the angle between them in real time and draws the corresponding arc, matching how a physical protractor is read. The displayed value is whatever unit is currently selected, and switching units re-renders the same geometric angle rather than re-measuring it.
Typing a number into the input field converts it using exact ratios: degrees to radians multiplies by pi/180, degrees to gradians multiplies by 400/360, and radians to gradians goes through degrees. All three fields update together so you can enter in any one unit and read the other two immediately.
No. The protractor here is drawn on-screen for you to align by eye or drag rays to match something you are looking at separately; it does not analyze an uploaded image to detect an angle automatically.
Gradians divide a full circle into 400 units instead of 360, so a right angle is exactly 100 gradians by definition. It is not a rounding artifact; 90 deg and 100 grad both represent exactly one quarter turn.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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