Types of Angles

Learn to identify and classify angles by their measure: acute, right, obtuse, straight, and reflex angles.

Elementary20 minLesson
Printable worksheet

Definition

An angle is formed when two rays share a common endpoint called the vertex. We measure angles in degrees (°).
Angles are classified by their measure:
TypeMeasureDescription
Acute0°<x<90°0° < x < 90°Smaller than a right angle
Rightx=90°x = 90°Exactly a quarter turn
Obtuse90°<x<180°90° < x < 180°Larger than right, smaller than straight
Straightx=180°x = 180°A half turn (forms a line)
Reflex180°<x<360°180° < x < 360°More than a straight angle

Try it now

What type of angle measures exactly 90°90°?

Worked Examples

A slice of pizza is cut at a 45°45° angle. What type of angle is this?
1

Read the angle measure

The angle is 45°45° → 45 degrees
2

Compare to benchmark angles

45°<90°45° < 90° → Less than a right angle
3

Classify the angle

Any angle between 0°0° and 90°90° is acute → Acute angle

Common Mistakes

Confusing acute and obtuse angles

Why it's wrong: Students mix up which is smaller and which is larger than 90°90°.

Correct: Compare with 90°90°, the corner of a sheet of paper: an acute angle is narrower than the corner (sharp, like a pencil tip), an obtuse angle is wider (open, like a laptop screen tilted back).

Thinking all angles in a square are different types

Why it's wrong: Students may not realize all corners of a square are identical right angles.

Correct: Every corner of a square or rectangle is a right angle (90°90°). That's what makes them "square"!

Forgetting about reflex angles

Why it's wrong: Students often only measure the smaller angle between two rays.

Correct: Every pair of rays creates TWO angles. The smaller one plus the larger one always equals 360°360°.

Thinking a straight angle isn't really an angle

Why it's wrong: It looks like just a line, so students don't recognize it as an angle.

Correct: A straight angle IS an angle - it's 180°180°, exactly half of a full rotation.

Watch a video explanation

The same topic explained by another teacher, if a video helps you more.

Types of Angles | Acute, Right, Obtuse, Straight, and Reflex

by Understand The Math

Watch on YouTube

Interactive Visual

Angle Explorer

Acute

Click the buttons to see different angle types.

Interactive Sandbox

Expression Calculator

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History

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Practice Problems

17 problems
Problem 1 of 17
Easy
What type of angle measures exactly 90°90°?

Why It Matters

Understanding angle types helps in many real-world situations:
  • Architecture: Builders use right angles to make sure walls are straight and corners are square
  • Sports: A basketball player's shooting angle affects whether the ball goes in
  • Design: Artists and designers use different angles to create visual effects
  • Navigation: Pilots and sailors use angles to determine direction and course
Recognizing angles quickly helps you understand shapes, directions, and measurements all around you!

Real World Applications

Clock Angles

The hands of a clock form different angle types throughout the day.

Example:

At 3:00, the hands form a 90°90° right angle. At 6:00, they form a 180°180° straight angle.

1Try It Yourself

Look at a clock showing 4:00.

How big is the angle between the hour and minute hands, and what type of angle is it?

Step 1: Write the mathematical expression

Neighboring hour marks are 30°30° apart, and there are 4 spaces from 12 to 4. Write an expression for the angle:

Skateboard Ramps

Skateboarders use ramps at different angles for tricks.

Example:

A beginner ramp might be at a 30°30° angle (acute), while a steep ramp for advanced tricks might be 60°60° (still acute, but steeper).

2Try It Yourself

A quarter-pipe ramp curves from the ground to a vertical wall.

What angle does the wall make with the ground?

Step 1: Write the mathematical expression

A vertical wall and horizontal ground meet at what angle?

Pizza Slices

When you cut a pizza, you create angles at the center.

Example:

A pizza cut into 8 equal slices has angles of 45°45° (acute) at the center.

3Try It Yourself

A pizza is cut into 6 equal slices.

What is the angle of each slice at the center?

Step 1: Write the mathematical expression

Divide a full circle by the number of slices:

Key Takeaways

  • 1An acute angle measures between 0°0° and 90°90° (smaller than a right angle)
  • 2A right angle measures exactly 90°90° and is marked with a small square
  • 3An obtuse angle measures between 90°90° and 180°180° (larger than right, smaller than straight)
  • 4A straight angle measures exactly 180°180° and looks like a straight line
  • 5A reflex angle measures between 180°180° and 360°360° (more than half a rotation)

Frequently Asked Questions

Compare it to the corner of a piece of paper (which is 90°90°). If the angle is smaller than the corner, it's acute. If it's larger, it's obtuse.
Compare it to the corner of a piece of paper (which is 90°90°). If the angle is smaller than the corner, it's acute. If it's larger, it's obtuse.
A 0°0° angle is when two rays overlap completely, pointing in the same direction. Some consider this no angle at all, while others call it a zero angle.
No! The angles in a triangle must add up to 180°180°. Two obtuse angles would already be more than 180°180° (each is greater than 90°90°), leaving no room for a third angle.

Glossary

Angle
The figure formed by two rays that share a common endpoint (vertex)
Vertex
The common endpoint where two rays meet to form an angle
Acute angle
An angle measuring less than 90°90°
Right angle
An angle measuring exactly 90°90°, often marked with a small square
Obtuse angle
An angle measuring more than 90°90° but less than 180°180°
Straight angle
An angle measuring exactly 180°180°, forming a straight line
Reflex angle
An angle measuring more than 180°180° but less than 360°360°
Degree
A unit of angle measurement; a full rotation is 360°360°
Today's challengeOne problem, three tries

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