Use Protractors for Angles
Lesson preview: the Mini Lesson and Vocabulary are open to everyone. Guided practice, exercises, the parent checklist and the printable PDF worksheet come with full access (free 7-day trial or membership).
Learning Objectives
- 1Identify acute, right, obtuse, and straight angles
- 2Measure angles using a protractor
- 3Classify angles as less than, equal to, or greater than 90°
Mini Lesson
An angle is formed where two rays meet at a point called the vertex. We measure angles in degrees (°) using a tool called a protractor. The size of the angle tells us how far one ray has turned from the other.
Types of Angles
- Right angle: exactly 90° — shown with a small square symbol at the vertex.
- Acute angle: less than 90° — a sharp, narrow angle.
- Obtuse angle: between 90° and 180° — a wide, blunt angle.
- Straight angle: exactly 180° — two rays pointing in opposite directions, forming a straight line.
Using a Protractor
- Place the center hole of the protractor exactly on the vertex of the angle.
- Align the base line (0°) of the protractor along one ray of the angle.
- Read the scale where the second ray crosses the numbered arc.
- Use the inner scale if the angle opens to the right; use the outer scale if it opens to the left.
Tip: always check whether your angle looks acute (sharp) or obtuse (wide) before reading the protractor. If your reading does not match the look of the angle, you have read the wrong scale.
Unlock the full HSEA system for 7 days.
Add your first kid profile and your 7 days start: every lesson in every grade, saved progress for each child. Nothing to set up, no card required, nothing to cancel.
- ✓ All 1,680 lessons, Grades 1–6, every subject
- ✓ Profiles + saved progress for every kid
- ✓ Printable lessons with answer key