Zellio.io

Angle Finder & Protractor

Drag the arms of the protractor to measure any angle on screen.

Processed locally — nothing is uploaded

About Angle Finder & Protractor

Drag the arms across a photo, or over a physical object held against the display, and the reading updates live. Suits a roof pitch taken from a picture, a joint in a drawing, or any angle that would otherwise be estimated by eye.

Measure any angle in degrees with an interactive on-screen protractor — drag the two arms to line them up and read the value live. It works right in your browser with no install.

Measure angles with an interactive on-screen protractor by dragging its arms over an image or object and reading the degrees live. It is useful for geometry homework, design layouts, woodworking references and any time you need to gauge an angle quickly.

Load a reference photo behind the protractor and drag the arms onto the angle you want to read. The readout updates as you move, so you can settle on the alignment rather than having to place it correctly first time.

Learn how this works

Everyday Calculations & Conversions Made SimpleConvert units and time zones, and calculate age, BMI, discounts and loan EMIs — a plain-English guide with free in-browser tools.7 min read

Frequently asked questions

How do I measure an angle on screen?

Position the protractor's centre on the angle's vertex and align one arm with the baseline, then read where the other arm crosses the scale. It is the same technique as a physical protractor, without needing one to hand.

How do degrees and radians relate?

A full turn is 360 degrees or 2π radians, so one radian is about 57.3 degrees. Maths and most programming languages default to radians, which is why trigonometry functions give unexpected answers when fed degrees.

What are complementary and supplementary angles?

Two angles are complementary if they sum to 90 degrees and supplementary if they sum to 180. Both come up constantly in geometry problems and in working out a missing angle from the ones you know.

Common Use Cases

  • •Measuring an angle in a photo or diagram on screen
  • •Checking homework geometry without a physical protractor
  • •Working out a cutting or mounting angle for a project

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Angle Finder & Protractor

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