Angle Builder with Kid Protractor
Drag the ray to build any angle from 0 to 360 degrees. See the angle type update live, toggle a protractor overlay, and try the matching challenge. Everything runs in your browser.
Try a preset
Less than 90°
Turn Language
Reference Guide
Types of Angles
Acute — less than 90 degrees. Think of a slightly open book.
Right — exactly 90 degrees. The corner of a piece of paper.
Obtuse — between 90 and 180 degrees. A door opened wide.
Straight — exactly 180 degrees. A perfectly flat line.
Reflex — between 180 and 360 degrees. More than a straight line.
Using a Protractor
1. Place the center mark of the protractor on the vertex (the point where the two rays meet).
2. Line up the base line of the protractor with one ray.
3. Read the scale where the other ray crosses the protractor. Start reading from 0 on the side that lines up with your base ray.
4. If the angle is larger than 180 degrees, measure the smaller angle first, then subtract it from 360.
Turn Language
Quarter turn = 90 degrees. Like a clock hand moving from 12 to 3.
Half turn = 180 degrees. Like a clock hand moving from 12 to 6.
Three-quarter turn = 270 degrees. Like a clock hand moving from 12 to 9.
Full turn = 360 degrees. A complete trip around the circle, back to where you started.
Measuring Angles
Every angle is measured in degrees. The symbol for degrees is a small raised circle: 90°.
A full circle contains 360 degrees. Half a circle is 180 degrees.
When two lines cross, the angles on opposite sides are always equal. These are called vertical angles.
Angles that add up to 90 degrees are called complementary. Angles that add up to 180 degrees are called supplementary.