On-screen protractor for measuring angles and ruler for measuring distances in images or on screen.
You can measure a paper drawing with a physical protractor; this tool measures whatever is on your screen instead. It overlays a protractor and a ruler on the page so you can read angles and distances straight from displayed content: the corner of a scanned plan, the slant of a text line, the width of a UI element in a screenshot. The thing most people get wrong is expecting real-world units. The readings stay in screen coordinates - degrees as drawn, distances in pixels - until you supply a known reference for scale.
A concrete input and expected output from the current implementation.
Input
Align the protractor's vertex on the corner where the bottom edge of a square in a screenshot meets its diagonal, one arm along the horizontal bottom edge and the other along the diagonal.
Expected output
45 degrees
A square's diagonal cuts the corner in half, so the angle between the horizontal bottom edge and the diagonal is 45 degrees, and the tool reports the angle between the two aligned lines as drawn in the image. Any line rising 1 unit for every 1 unit it runs makes the same angle.
The protractor is an overlay with a vertex and two arms. You place the vertex on the corner or intersection you care about, then align each arm with one of the two edges, and the tool reports the angle between the arms in degrees. The reading is the angle as it appears in the image plane, which is what makes it useful for checking alignment, skew, and draftsmanship.
The ruler is an overlay with two endpoints. You set one endpoint at the start of the span and the other at its end, and the tool reports the distance between them. On screen that distance is in pixels, so the number depends on the image resolution and the page zoom level. Converting it to inches or millimeters requires a known-length object in the same image to scale against.
Not from the photo alone. The ruler measures what is on screen in pixels, so a real-world size only comes out if you can calibrate: photograph a known-size object in the same frame and scale by its pixel width. A credit card is 85.60 x 53.98 mm, so a card photographed 1200 pixels wide gives about 0.071 mm per pixel to scale other measurements by.
No. The tool reads the angle between the two lines you align, exactly as they are drawn on screen. If the camera faced the surface at an angle, real straight lines can appear tilted in the image, and the reading reflects that tilt, not the true angle. Photograph the surface head-on, or use readings only to compare angles within the same image.
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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