Right, acute and obtuse — learn all about angles! 🍭
A right angle is exactly 90°. It looks like the corner of a square. There are four right angles in a full turn of 360°. Architects use right angles every day when designing buildings!
An angle is the amount of turn between two lines that meet at a point. We measure angles in degrees (°).
We use a protractor to measure angles precisely.
| Type | Size | How to spot it |
|---|---|---|
| Right angle | Exactly 90° | Corner of a square — shown with a small square symbol |
| Acute angle | Less than 90° | Smaller than a right angle — sharp and pointy |
| Obtuse angle | More than 90° | Bigger than a right angle but less than 180° |
A straight line is actually a straight angle = 180°.
Angles on a straight line add up to 180°.
Angles around a point add up to 360°.
We mark right angles with a small square. Some shapes have lots of right angles!
| Shape | Right angles |
|---|---|
| Square | 4 |
| Rectangle | 4 |
| Triangle | 0, 1, or none (right-angled triangle has 1) |
| Turn | Degrees | Right angles |
|---|---|---|
| Quarter turn | 90° | 1 |
| Half turn | 180° | 2 |
| Three-quarter turn | 270° | 3 |
| Full turn | 360° | 4 |
Without a protractor you can compare angles by looking at them. Use a right angle tester (corner of paper) to check if an angle is right, acute or obtuse.
What type is a 45° angle?
Two angles on a straight line. One is 60°. Find the other.
A triangle has angles 60° and 50°. Find the third.
How many right angles does a rectangle have?
An angle of 90° is cut from a full turn (360°). Remainder = ?
Drag the slider to change the angle. Watch it draw on the canvas and see the type!
Enter one angle on a straight line:
Enter: 1 = right angle, 2 = acute, 3 = obtuse
Angles on a straight line add up to 180°. Find the missing angle.
Angles in a triangle add up to 180°. Find the missing angle.
How many right angles does each shape have?
Angles around a point add up to 360°. Find the missing angle.
First 10: enter 1=right, 2=acute, 3=obtuse. Last 10: find the missing angle on a straight line.
Name the type of each angle: enter 1=right, 2=acute, 3=obtuse.