Online protractor
A full-circle protractor for measuring angles on screen: the corner of a printed shape, a line in a photo, or the slope of something held up to the display.
How to measure an angle
- Drag the dial by its face so its center sits on the corner you want to measure.
- Drag arm A along one side of the angle.
- Drag arm B along the other side.
The large number is the angle going anticlockwise from A to B, which is the number printed on the dial where B points when A is on 0. The small number beside it is the same angle measured the other way round, so a 120° reading also shows 240°. The two always add up to 360°.
Handy controls
- 0°, 45°, 90°, 180° move arm B to that angle from arm A, for checking right angles and straight lines.
- The small diamond on the rim makes the dial bigger or smaller. A bigger dial is easier to read precisely.
- The lock stops the dial from moving while you adjust the arms.
- With an arm selected, the arrow keys turn it one degree at a time, and holding Alt turns it by a tenth of a degree.
Measuring an angle in a photo
Use Measure a photo in the tool bar (under More on a phone) to open a picture behind the protractor. Unlike lengths, angles don't depend on the screen's size, so you can measure angles in a photo without calibrating first. Keep the photo straight on, though: a photo taken at a slant changes the angles in it.
Reading a protractor
Angles under 90° are acute, exactly 90° is a right angle, between 90° and 180° is obtuse, and over 180° is a reflex angle. A straight line is 180°, and a full turn is 360°.