Types of Angles: Acute to Reflex

G8Types of Angles

Acute, right, obtuse, straight, reflex.

Angles measure turn, in degrees. Five families cover every angle.

The five angle families.

Acute < 90°

Right = 90°

Obtuse 90–180°

Straight = 180°

Reflex > 180°

A full turn is 360° · half turn 180° · quarter turn 90°.

Learn the Families

1Compare with 90°.

Smaller than a square corner → acute. Exactly 90° → right angle (marked with a small square).

< 90° acute

2Compare with 180°.

Between 90° and 180° → obtuse. Exactly 180° → straight line.

90–180° obtuse

3Bigger than 180°?

Reflex — the angle going the long way round, up to 360°.

> 180° reflex

💡 Key IdeaAngles measure turn, not length — long arms don't make a bigger angle.

Worked Example

Classify each angle.

72°

acute

148°

obtuse

90°

right angle

203°

reflex

Watch Out! Common Mistakes

Longer arms = bigger angle.

Wrong! The angle is the amount of turn between the arms. Arm length changes nothing.

Calling 180° obtuse.

180° = obtuse ✕

Wrong! Obtuse is between 90° and 180°. Exactly 180° is a straight angle.

Forgetting reflex exists.

Remember! Angles over 180° (up to 360°) are reflex — like the big way round a clock face.

⬇ Cheat Sheet

TYPES OF ANGLES

Acute < 90° · right = 90° · obtuse 90–180°
Straight = 180° · reflex > 180°
Full turn = 360°.
Angle = turn, not arm length.

Example: 72° acute · 148° obtuse · 203° reflex

📄 Free printable: Download the Types of Angles cheat sheet (PDF) — keep it by your child's desk.

Quick summary

Acute < 90°; right = 90°; obtuse between 90° and 180°.
Straight = 180°; reflex > 180° (up to 360°).
A full turn is 360°.
The angle is the turn between the arms — their length is irrelevant.

Frequently asked questions

What are the five types of angle?

Acute (less than 90°), right (exactly 90°), obtuse (between 90° and 180°), straight (exactly 180°) and reflex (more than 180°).

What is a reflex angle?

An angle bigger than 180° — measuring the long way round, like three-quarters of a turn (270°).

Does drawing longer lines make an angle bigger?

No. The angle measures the amount of turn between the two arms; the arms' length doesn't change it — a key misconception this lesson corrects.

G9 Measuring and Drawing Angles

Types of Angles