General / Browser tools

Online Protractor

Measure an on-screen angle with two draggable arms and an optional local image, in 180° or 360° mode.

Online Protractor: Measure an on-screen angle with two draggable arms and an optional local image, in 180° or 360° mode. Runs 100% locally in your browser with zero server file uploads.

Category
Everyday tools
Runs
In your browser
Cost
Free · no sign-up
Availability
Ready to use
On-screen protractorLocal processing

Runs entirely in your browser

60.0°

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Place the centre on the vertex, then drag each arm along an edge. Angles are scale-free, so screen calibration is unnecessary. Perspective or a distorted photograph can change the apparent angle; use a straight-on image. The image stays on your device.

Measure lengths with the online ruler

Angle conventions

A full turn is 360 degrees. The 180° mode reports the smaller angle between the arms, from 0 to 180 degrees. The 360° mode measures anticlockwise from arm 1 to arm 2; overlapping arms report zero.

Image alignment

The image keeps its aspect ratio and stays on your device. Supported images are PNG, JPEG and WebP up to 15 MB. Drag the centre to the vertex before aligning the arms; no length calibration changes the angle.

How to use it

  1. Optionally choose a PNG, JPEG or WebP reference image.
  2. Move the centre to the vertex and drag the arms along the edges.
  3. Read the smaller angle or the anticlockwise angle from arm 1 to arm 2.

Privacy & limitations

Your inputs stay in this browser. Nothing you enter is uploaded or saved.

Related tools

Online Ruler

Frequently asked questions

Do I need screen calibration?

No. Angles compare directions and are independent of uniform scale. Unlike length measurements, they do not need a known-size object.

Why does a photographed angle look different?

Perspective and image distortion can change the apparent angle. Use a straight-on view of the plane you want to measure. The tool measures the displayed image, not a corrected 3D angle.

Can I use it with a keyboard?

Yes. Sliders control both arms and the centre position. An opacity slider helps align arms over an image.

Free tool · runs in your browser · no account required