What is an angle?

An angle is made when two straight lines meet at a point. The point where they meet is called the vertex. Each line is called an arm (or side) of the angle.

We write an angle with the symbol ∠. For example, ∠ABC means the angle with vertex at B and arms BA and BC.

How we measure angles

Angles are measured in degrees (°). A full circle is 360°.

Use a protractor to measure an angle. Place the hole on the vertex, line up one arm with 0°, and read the number where the other arm crosses the protractor.

Types of angles

• Acute angle: less than 90° (small sharp angle).
• Right angle: exactly 90° (square corner).
• Obtuse angle: more than 90° and less than 180° (wide angle).
• Straight angle: exactly 180° (a straight line).
• Full turn: 360° (a full circle).

Everyday examples

• Open book corner — right angle (90°).
• Partly open door — obtuse angle (>90°).
• Pencil tip with two lines close — acute angle (<90°).
• Clock hands at 6 o’clock — straight angle (180°).

How to read a simple protractor (steps)

1. Place the centre hole of the protractor on the vertex of the angle.
2. Line up one arm with the 0° line on the protractor.
3. Look at where the other arm crosses the protractor scale — that number is the angle in degrees.

Practice — try these

1. Look at the angle: 45°. Is it acute, right, or obtuse?
2. Which angle is 90°? Choose: 30°, 90°, 150°.
3. If two angles add to 90°, they are called _______ angles.
4. Which is larger: 100° or 120°? What type is 120°?
5. Draw (or imagine) a straight line. What is the angle measure?

Good to remember

• Angles tell us how much one line has turned from another.
• Use simple objects (books, doors, clocks) to find real-life angles.
• Practice with a protractor and draw angles to learn faster.